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2019

159. J. C. Fernandes, N. R. Agrawal, F. O. Aljirafi,…S. R. Raghavan

158. H. Guo,…K. C. DeMella, S. R. Raghavan, Z. H. Nie

157. K. C. DeMella, S. R. Raghavan

156. A. Gargava, S. Ahn, W. E. Bentley, S. R. Raghavan

154. M. Omarova,…S. R. Raghavan, V. T. John

153. V. S. Balachandran,…S. R. Raghavan,…G. John

152. J. P. Goertz, K. C. DeMella, B. Thompson, I. White, S. R. Raghavan

151. J. Zheng,…K. C. DeMella, S. R. Raghavan, C. S. Wang

High-fluorinated electrolytes for Li-S batteries.
Advanced Energy Materials, 9, 1803774 (2019)

150. M. T. Logun, M. B. Dowling, S. R. Raghavan,….L. Karumbaiah

149. H. Guo,…K. C. DeMella, S. R. Raghavan, Z. H. Nie

Self-assembly of surfactants has been well-studied in water, but not in other polar solvents. This paper shows for the first time that one can form long chains (‘wormlike micelles’) by self-assembly in polar solvents like glycerol. The resulting fluids remain viscoelastic at temperatures down to -20°C. They could be useful as anti-icing sprays for aircraft.

This paper demonstrates a capsule that can protect its contents with a hermetic seal, i.e., one that is perfectly leak-proof. This is done by making the capsule shell out of a wax with a defined melting temperature. Above this temperature, the shell melts and the contents are released in a burst. 

This paper is part of our ongoing efforts to clear oil spills using food-grade ‘dispersants’. All dispersants contain an organic solvent, but the role of this solvent is usually neglected. It is shown in this paper that the solvent can significantly impact the efficiency with which the oil is dispersed into seawater. Criteria for selecting the optimal solvent are presented. 

Making gels by 3D-printing requires special ‘inks’ and an expensive printer. This paper shows a simple way to create gels of the biopolymer alginate. The key is to induce gelation by an electric field, a process called ‘electroformation’. It can be done in any lab at low cost and it yields robust gels in precise shapes and patterns. Cells can be readily embedded in these gels. 

The capsule in this paper is designed with catalytic particles in its core. When a fuel is present in the water, a reaction occurs in the capsule, generating oxygen gas. The gas bubbles inflate the capsule until it finally explodes and ejects the core – behavior that is reminiscent of the pufferfish and jellyfish. 

2018

148. S. Gharazi, B. C. Zarket, K. C. DeMella, S. R. Raghavan

147. J. Zheng,…S. R. Raghavan, J. Wang, K. Xu, C. S. Wang

146. O. Owoseni,…S. R. Raghavan, A. Bose, V. T. John

145. J. C. Athas, C. P. Nguyen, S. Kummar, S. R. Raghavan

144. S. R. Raghavan, N. J. Fernandes, B. H. Cipriano

143. S. D. Lacey,…S. R. Raghavan, J. W. Connell, Y. Lin, L. Hu

142. M. K. Rhoads,…S. R. Raghavan, G. F. Payne, W. E. Bentley

This paper shows how to create a hydrogel that has many zones, each of which has different mechanical properties. Such multi-zone materials are often found in nature such as the beak of a squid or the spinal discs in our spinal cord. The gel above has four zones, which stretch to different extents. The stiffest zone has a modulus 100 times that of the softest zone. 

This paper reports two unusual findings regarding the spontaneous folding of certain gel strips. First, these gels are shown to fold when divalent cations like Ca2+ are added to the water. Second, the rectangular gel folds along its long-axis, as shown above. In contrast, typical gels fold along their short-axis.

2017

141. C. Arya, C. A. Saez, H. Huang, S. R. Raghavan

140. J. Wang, Y. Feng, N. R. Agrawal, S. R. Raghavan

139. A. X. Lu, H. Oh, J. Terrell, W. E. Bentley, S. R. Raghavan

138. B. C. Zarket and S. R. Raghavan

137. Y. Zhang,…S. R. Raghavan, D. Zhang, V. T. John

136. A. Chaturvedi, M. B. Dowling,…S. R. Raghavan, M. M. Narayan

This work is inspired by the architecture of eukaryotic cells, which are containers with smaller containers (organelles) in them. In an attempt to mimic this architecture, this paper describes the synthesis of multicompartment capsules (MCCs). The MCCs are made from common biopolymers by a microfluidic approach that uses only water and gas. The number of inner compartments and the contents of each can be tuned; the contents can be particles, enzymes, or bacteria. It is shown that, when two strains of bacteria are placed in separate compartments, a signal from one can trigger a response in the adjacent one.

Many materials in nature, including the onion, the egg, and tissues in our body have multiple concentric layers. To mimic this architecture, a simple synthesis technique is shown in this paper that can yield onion-like multilayered polymer capsules. The technique proceeds ‘inside-out’, i.e., each layer grows outward from the previous one. The composition and thickness of each polymer layer can be varied, and by this means, the release of drugs stored in the capsule lumen can be controlled.

This work was highlighted in a variety of news media.

2016

135. C. Arya, H. Oh, S. R. Raghavan

134. M. B. Dowling, I. MacIntire,…S. R. Raghavan,…M. M. Narayan

133. J. C. Athas, C. P. Nguyen,…S. R. Raghavan

Enzyme-triggered folding of hydrogels: Towards a mimic of the Venus flytrap.
ACS Applied Materials & Interfaces, 8, 19066 (2016)

132. A. Gargava, C. Arya, S. R. Raghavan

Smart hydrogel-based valves inspired by the stomata in plants.
ACS Applied Materials & Interfaces, 8, 18430 (2016)

131. H. Oh, A. X. Lu,…S. R. Raghavan

130. A. X. Lu,…Z. H. Nie, D. L. DeVoe, S. R. Raghavan

129. R. Ghaffarian,…H. Oh, S. R. Raghavan, S. Muro 

128. Y. C. Kuo,…W. D. D’Souza, S. R. Raghavan

One kind of immune cells in our body are the ‘killer’ cells, which target pathogens and deliver a deadly dose of proteins to kill them. In the same vein, this paper puts forward the idea of ‘killer capsules’ that can target another kind of capsule. When the killer is near its target, it delivers a molecule that destroys the target, as shown in the above movie.

This paper describes a hydrogel that folds from a flat sheet to a tube when an enzyme is added to the water at low concentrations. Such self-folding gels are reminiscent of natural structures such as the Venus flytrap, a plant that folds its leaves to entrap its prey (top images). In the bottom images, the self-folding gel is used as the hinge between two rigid gels in a mimic of the Venus flytrap.

This paper is our first foray into the field of robotics. It shows the preparation of ‘micromotors’, which can swim by harvesting a chemical fuel in the water. The path of the motor can be controlled by a magnet. The motor can thus be directed to pick up a cargo, move it to a destination, and finally drop off this cargo.

Valve-like structures on plant leaves called stomata regulate the flow of water. This paper reports polymer gel-based valves inspired by the stomata. The  central pore in the gel opens and allows flow of a liquid only if the liquid satisfies certain properties. For example, in one design, the pore opens to let hot water through, but not cold water. In a second design, water will flow through only if it is both hot and acidic.

2015

127. D. A. Riehm,…S. R. Raghavan, A. V. McCormick

126. K. R. Pandit,…S. R. Raghavan, I. M. White

125. M. S. Wiederoder,…S. R. Raghavan, D. L. DeVoe

124. J. S. Arora,…S. R. Raghavan, D. Blake, V. T. John

123. M. B. Dowling, I. C. MacIntire,…S. R. Raghavan

122. H. Oh, N. Yaraghi, S. R. Raghavan

121. G. Peters,…S. R. Raghavan, J. T. Davis

G4-quartet.M+ borate hydrogels.
JACS, 137, 5819 (2015)

120. K. Q. Jiang,…D. L. DeVoe, S. R. Raghavan

Microfluidic generation of uniform water droplets using gas as the continuous phase.
Journal of Colloid and Interface Science, 448, 275 (2015)

119. K. R. Pandit,…S. R. Raghavan, I. M. White

118. M. B. Dowling,…S. R. Raghavan, D. R. King

This paper explores an idea for the self-repair of leaks from a tube. An oily fluid flows through the tube, which is submerged in water. If the tube is damaged, the oil leaks out into the water. At this point, ‘gelator’ molecules in the oil get activated, and they assemble into a fibrous network, thereby sealing the leak. This process is reminiscent of blood clotting, where again blood platelets are activated to aggregate only at the site of a wound.

This paper extends our work on amphiphilic polymers that can stop severe bleeding and thereby achieve hemostasis. Here, the polymer is used to make a hemostatic foam, which is sprayed onto a bleeding wound in a pig liver. The foam is able to stop the bleeding without any compression being applied. This technology is being commercialized by Gel-e, Inc., a company run by Matt Dowling, who was the first author of this paper.

This work was featured in a variety of scientific media including C&EN.

Microfluidic techniques are commonly used to form uniform droplets of water. However, this is typically done using water and an immiscible second liquid, i.e., an oil. This paper shows that the oil can be avoided and replaced with air, while still generating uniform aqueous droplets. As demonstrated in the above movie, water droplets at the end of an inner capillary are sheared off by an annular flow of air.

2014

117. R. Zheng,…S. R. Raghavan, N. Pesika, V. T. John

116. Z. Wei,…J. Athas,…S. R. Raghavan, T. Li, Z. H. Nie

115. C.-Y. Cheng,…S. R. Raghavan, S.-H. Tung

114. N. A. Burns,…S. R. Raghavan, S. A. Khan

113. J. C. Athas, K. Jun,…V. T. John, S. R. Raghavan

112. Y-C. Kuo, C-W. Hung,…S. R. Raghavan, W. D. D’Souza

111. B. H. Cipriano, S. J. Banik,…R. M. Briber, S. R. Raghavan

110. A. K. Higham, C. A. Bonino, S. R. Raghavan, S. A. Khan 

109. V. Javvaji, M. B. Dowling,…S. R. Raghavan

108. K. K. Diehn, H. Oh,…R. G. Weiss, S. R. Raghavan

107. Y. Liu,…V. Javvaji,…S. R. Raghavan,…G. F. Payne

Oil spills on the ocean are usually cleared by spraying dispersants, which break up the oil into small droplets. In typical dispersants, some of the components can be toxic. In this paper, an alternative dispersant is designed – one made from food-grade, non-toxic components. The key components are lecithin (a lipid extracted from soy) and Tween 80 (a surfactant used in ice cream), and the two work synergistically to form stable emulsions of crude oil in seawater.

This work was highlighted by a variety of news media, including the UMD Diamondback newspaper.

Gels that absorb a lot of water, called superabsorbent gels, are used in many products, including diapers. This paper reports a new kind of superabsorbent gel that beats the world record for water-absorption – it can absorb 3000 times its weight in water. The gel is made from commercial monomers using a variation of the typical polymerization strategy. In addition to its superabsorbency, the gel is also notable for its mechanical robustness. In its unswollen state, the gel can be stretched up to 14 times its original length.

This paper was one of the ‘Most Read‘ papers in Macromolecules in 2014. 

Citations: > 100 (Google Scholar)

This paper generalizes our results on the effects of amphiphilic polymers on biological cells. Such polymers can embed their hydrophobic side chains in cell membranes. Thereby, the cells get connected into a 3-D network, i.e., into a gel. Gelation in this manner is shown with various cell types, including blood. The end result is a self-assembled network in which the cells form the nodes, much like in a tissue. Gelation can be reversed by adding molecules that capture the hydrophobes.

This work was highlighted by Biomaterials Science.

Many ‘gelator’ molecules self-assemble into long fibers, which entangle to produce molecular gels. Such gels form in some organic solvents, but not in others. Can one predict a priori if a gel would arise in a given solvent? This paper puts forward a framework to predict molecular gelation using thermodynamic parameters of the solvents. On a 3-D plot of Hansen solubility parameters, the solvents in which gels are formed cluster into spherical regions, as shown.

The MATLAB program developed for this paper is freely available to the scientific community. If interested, email Prof. Raghavan.

Citations: > 100 (Google Scholar)

2013

106. Y. Chen, V. Javvaji, I. C. MacIntire, S. R. Raghavan

105. H. Oh, V. Javvaji,…D. Danino, S. R. Raghavan

104. A. X. Lu, K. Q. Jiang, D. L. DeVoe, S. R. Raghavan

103. C. Arya,…S. R. Raghavan, S. P. Forry

102. N. Yan,…S. R. Raghavan, Y. Fang, R. G. Weiss

101. M. B. Dowling, A. S. Bagal, S. R. Raghavan

100. P. Venkataraman,…S. R. Raghavan,…V. T. John

  99.  H. Oh, A. M. Ketner,…D. E. Falvey, S. R. Raghavan

  98.  N. Yan,…K. K. Diehn, S. R. Raghavan,…R. G. Weiss

  97.  V. R. Basrur, J. Guo, C. S. Wang, S. R. Raghavan

  96.  H. Shi, W. Ge, H. Oh,…S. R. Raghavan, J. L. Zakin

  95.  H-Y. Lee, K. Hashizaki, K. K. Diehn, S. R. Raghavan

  94.  A. Gupta,…S. R. Raghavan, W. E. Bentley

Vesicles are nanoscale (~ 100 nm) containers that find application in drug delivery. This paper describes a simple way, using cheap, widely available molecules, to create vesicles that are responsive to light. When exposed to UV light, the vesicles are transformed into much smaller (~ 5 nm) spherical micelles.

This paper puts forward the idea of capsules that self-destruct after a set time. The capsules have enzymes in their lumen, which slowly degrade the capsule shell. As the microscale structures (termed ‘motherships’) degrade, they release their internal cargo of nanoscale vesicles (termed ‘babyships’). The time it takes for the capsule to degrade can be tuned by the internal enzyme concentration.

This paper represents the culmination of our work on  fluids with light-tunable flow properties. It reports a simple, surfactant-based fluid whose viscosity can be reversibly switched a million-fold by two kinds of light. UV light increases the viscosity while visible light decreases it back to its initial value. 

Lithium-ion batteries currently use liquid electrolytes for their high conductivity, but the liquids can leak out of the battery. This paper reports electrolytes with liquid-like conductivities but solid-like mechanical properties. This combination of properties is achieved by gelling a Li+ salt solution using a molecular gelator coupled with silica nanoparticles. The gel is strong enough that it can be held in one’s hand.  

2012

93.    K. Jiang,…S. R. Raghavan, D. L. DeVoe

92.    J. H. Lee,…S. R. Raghavan, R. Blumenthal

91.    Y. Liu, V. Javvaji, S. R. Raghavan, W. E. Bentley, G. F. Payne

90.    O. A. Ogunsola,…R. L. Bronaugh, S. R. Raghavan

89.    H-Y. Lee, H. Oh, J. H. Lee, S. R. Raghavan

88.    S. J. Banik, N. J. Fernandes, P. C. Thomas, S. R. Raghavan

87.    S. R. Raghavan, J. F. Douglas

86.    P. Sahoo,…S. R. Raghavan, P. Dastidar 

Gel sculpture: Moldable, load-bearing and self-healing supramolecular gel.
Chemistry: A European Journal, 18, 8057 (2012)  (Cover)

85.    Y. Liu,…S. R. Raghavan, W. E. Bentley, G. F. Payne

84.    G. DeCastro, M. B. Dowling, S. R. Raghavan,..G. Bochicchio 

83.    K. Sun, H. Oh, J. F. Emerson, S. R. Raghavan

82.    K. Jiang, P. C. Thomas,…D. L. DeVoe, S. R. Raghavan

This paper shows a simple, new method to synthesize ‘hybrid gels’ where different zones of the gel have distinct properties. For example, one zone is ‘written’ in a pattern (‘UMD’) within the other. Initially, the hybrid gel appears homogeneous and the pattern is hidden. Subsequently, the pattern can be revealed either optically or thermally.

This work was featured by New Scientist magazine.

This paper reports two interesting discoveries. First, a mixture of a diacetylenic surfactant and an alcohol is shown to form a gel of close-packed vesicles. Next, when this gel is diluted, the vesicles transform first into helical ribbons and then into closed tubules. The transition of ribbons to tubules is visualized in real-time using optical microscopy.

Nanoscale structures that can penetrate through skin have been highly sought after. In this regard, there are many reports on ‘flexible’ liposomes, which are believed to be able to squeeze through pores in the Stratum Corneum, i.e., the outermost layer of skin. This paper examines the structure of a typical formulation of ‘flexible’ liposomes and finds that the liposomes are not really flexible. Instead, the samples are in fact mixtures of liposomes and micelles. Penetration through skin is indeed achieved, and an alternative hypothesis is advanced in the paper as to why this occurs.  

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Self-assembly into chains is ubiquitous in nature: e.g., wormlike micelles of surfactants, protein filaments such as F-actin, and fibers of molecular gelators. The chains are not cross-linked; yet, all these systems behave as elastic gels. Why? This paper suggests that gelation can occur simply by physical entanglements if the chains are long and stiff.

Times Cited: > 100 (Google Scholar)

Polydimethylsiloxane (PDMS or silicone) is an inert, nontoxic elastomer. This paper uses a microfluidic approach to create uniform microbeads of PDMS. Moreover, an oxygen-sensitive phosphorescent dye is embedded in these beads during synthesis. The resulting beads can then be used to sense the local oxygen concentration in a sample.

Blood is separated from serum by centrifugation in tubes that contain a thixotropic gel. This gel forms a weak barrier between the phases based on density differences. A new concept is described in this paper, which is to make the gel UV-curable. The gel can then be solidified by UV light, thus creating a strong, ‘perfect’ barrier between blood and serum. This technology has been licensed by a startup company, BioSpecimen Technologies, that is being run by our collaborator, Dr. Jane Emerson from USC.

This work was selected for the Back Cover of the issue by J. Mater. Chem. and was highlighted in a variety of news media, including Chemistry World.

2011

81.    P. C. ThomasS. R. Raghavan, S. P. Forry

Regulating oxygen levels in a microfluidic device.
Analytical Chemistry, 83, 8821 (2011)

80.    V. Javvaji, A. G. Baradwaj, G. F. Payne, S. R. Raghavan

79.    P. C. Thomas, B. H. Cipriano, S. R. Raghavan

78.    H. Y. Lee, K. K. Diehn, K. Sun, T. Chen, S. R. Raghavan

77.    K. Q. Jiang, C. Xue,…D. L. DeVoe, S. R. Raghavan

76.    H. Shi,…S. R. Raghavan, J. L. Zakin

75.    J. E. St.Dennis,…S. R. Raghavan, V. T. John

74.    M. B. Dowling, R. Kumar, M. A. Keibler,…S. R. Raghavan

73.    L. Ziserman, H.-Y. Lee, S. R. Raghavan, A. Mor, D. Danino

72.    H. Y. Lee, K. R. Tiwari, S. R. Raghavan

71.    M. B. Dowling, V. Javvaji, G. F. Payne, S. R. Raghavan

70.    P. Sahoo, D. Kumar, S. R. Raghavan, P. Dastidar 

Supramolecular synthons in designing low molecular mass gelling agents.
Chemistry: An Asian Journal, 6, 1038 (2011)   (Cover)

This paper shows how a biopolymer such as alginate can be gelled using light. This is done without any chemical modification to the polymer backbone. The idea is to mix the polymer with certain photoactive molecules and CaCO3 particles. Under UV light, Ca2+ ions are generated, which gel the polymer. Gels can be formed in precise patterns using a photomask.

This paper was selected for the cover of Langmuir.

This paper shows the application of a hydrogel containing laponite nanoparticles in separations. The particles have a strong affinity for cationic solutes. Thus, the gel selectively removes a cationic dye from a mixture of cationic and anionic dyes (see above).

This paper describes a simple fluid whose viscosity could be reversibly altered by shining light at different wavelengths. The initial yellow fluid contains commercially-available lipids and photosensitive molecules dissolved in cyclohexane. The molecules self-assemble into long chains, and thus the fluid has a high viscosity. Upon irradiation with UV light, the molecules re-assemble into shorter chains, and hence the red fluid has a lower viscosity. Next, upon irradiation with visible light, the original yellow fluid with a high viscosity is recovered.

Citations: > 100 (Google Scholar)

Micro-manufacturing implies the use of a microfluidic chip as a miniature factory. Towards this end, this paper uses a chip that takes in a polymer (chitosan) solution as feed, creates polymer droplets, converts them into particles, and then connects those on-chip into functional microchains. Magnetic and/or fluorescent chains can thus be created.

This paper was selected as a Frontispiece by Small.

This paper demonstrates capsules that non-invasively sense solution pH and temperature. The capsules contain polymerized vesicles of a diacetylene-based amphiphile. Due to the vesicles, the capsules show a blue or red color under different conditions.

This paper shows that an amphiphilic polymer is able to convert liquid blood into a gel (see above) by a self-assembly mechanism. The same polymer acts as a ‘hemostatic‘ agent, i.e., it rapidly stops bleeding from severe injuries in animal models. This technology won the Invention of the Year award at UMD in 2009. It is being commercialized by Gel-e, Inc., a company run by Matt Dowling, who was the first author of this paper.  

This work was highlighted in a variety of scientific media including C&EN.

Citations: > 150 (Google Scholar)

2010

69.    J. B. Borak, H-Y. Lee, S. R. Raghavan, D. E. Falvey 

68.    H-Y. Lee, K. K. Diehn, S. W. Ko, S-H. Tung, S. R. Raghavan

67.    S. R. Jadhav, P. K. Vemula, R. Kumar, S. R. Raghavan, G. John

66.    C. Ropp,…S. R. Raghavan, E. Waks, B. Shapiro

65.    J. S. Hong,…L. E. Locascio, S. R. Raghavan, M. Gaitan

64.    K. Sun and S. R. Raghavan

63.    R. Kumar, A. M. Ketner, S. R. Raghavan

62.    R. Kumar and S. R. Raghavan

Can salts be dissolved in oil? Indeed they can, as shown by this paper, provided a lipid is also present. Moreover, the type of cation has a key influence on the self-assembly of the lipid. While Na+ has no effect, divalent cations like Ca2+ and trivalent cations like La3+ induce the lipid to form long chains. These chains entangle to produce an organogel.

This paper shows that a mixture of clay nanoparticles and a polymeric surfactant show thermogelling, i.e., a transition from liquid to gel upon heating to 75°C. The effect is synergistic, i.e., it is exhibited by the mixture, but not the individual components. The hypothesis advanced in the paper for the thermogelling is that it is induced by ‘depletion interactions‘, which arise between the nanoparticles when the surfactant forms micelles at high temperatures.

This paper reports a simple recipe for an oil-based fluid whose viscosity could be tuned by shining light. The fluid contains lipid molecules that self-assemble into long cylindrical chains initially. Irradiation with UV light alters the geometry of the lipids, which makes them re-assemble into short cylinders, causing a 1000-fold drop in viscosity.

2009

61.    P. C. Thomas,…S. R. Raghavan, S. P. Forry

60.    L. Ziserman,…S. R. Raghavan, D. Danino

59.    W-C. Lai, S-C. Tseng, S-H. Tung, Y. E. Huang, S. R. Raghavan

58.    K. Sun, R. Kumar, D. E. Falvey, S. R. Raghavan

57.    P. Sahoo,…S. R. Raghavan,…P. Dastidar

56.    M. B. Dowling, J. H. Lee, S. R. Raghavan

55.    B. H. Cipriano, T. Kashiwagi, X. Zhang, S. R. Raghavan

54.    J. H. Lee, D. Danino, S. R. Raghavan

53.    B. D. Frounfelker,…D. Danino, S. R. Raghavan

52.    R. Kumar and S. R. Raghavan

This paper shows how to endow a suspension of clay nanoparticles with photoresponsive properties. The low-viscosity suspension (sol) contains a photoacid generator (PAG). The particles are discrete and stabilized. When irradiated with UV light, the PAG generates acid, and the lowering of pH induces the clay particles to assemble into a gel network.

Vesicles (size ~ 100 nm) of oleic acid are embedded in gelatin gels (Jello). The gel has a bluish color due to light scattering from the vesicles. When the gel is contacted above it in the vial with water at pH > 10, the vesicles are transformed into smaller micelles (size ~ 5 nm). The micellar zone is colorless and its interface with the bluish vesicle zone can be seen.

2008

51.    B. H. Cipriano, A. K. Kota,…H. A. Bruck, S. R. Raghavan

50.    T. Kashiwagi, M. Wu, K. Winey, B. H. Cipriano, S. R. Raghavan,…

49.    S. Talwar, L. Scanu, S. R. Raghavan, S. A. Khan

48.    S-H. Tung and S. R. Raghavan

47.    S.-H. Tung, H.-Y. Lee, S. R. Raghavan

46.    S-H. Tung, Y-E. Huang, S. R. Raghavan

45.    J. S. Hong,…L. Locascio, M. Gaitan, S. R. Raghavan

Carbon nanotubes (CNTs) and nanofibers (CNFs) impart electrical conductivity to polymers. However, the conductivities of extruded polymer/CNT and polymer/CNF composites can be very low initially. This paper shows that annealing the composites can restore the conductivity due to the re-formation of connections between the particles.

Citations: > 150 (Google Scholar)

Self-assembly of vesicles (nanoscale containers) in water is well-known. But their counterparts in oil (i.e., nonpolar organic liquids) are very rare. This paper demonstrates a new way to form ‘reverse vesicles’ in oil. The approach is very simple and involves the self-assembly of two lipids, one with two long (C18) tails and the other with two short (C4) tails.

Citations: > 80 (Google Scholar)

2007

44.    A. K. Kota,…S. R. Raghavan, H. A. Bruck

43.    R. Kumar,…D. Danino, S. R. Raghavan

42.    B. H. Cipriano, T. Kashiwagi, S. R. Raghavan,…

41.    A. K. Kota, B. H. Cipriano,…S. R. Raghavan, H. A. Bruck

40.    E. J. Danoff,…S. R. Raghavan, D. S. English

39.    A. M. Ketner, R. Kumar, T. Davies,…S. R. Raghavan

38.    S.-H. Tung, Y.-E. Huang, S. R. Raghavan

37.    G. F. Payne and S. R. Raghavan

36.    C. Zhu, L-Q. Wu,…S. R. Raghavan, G. F. Payne

This study demonstrates for the first time that ‘wormlike micelles’ (long self-assembled chains) can be formed in water by a zwitterionic surfactant (i.e., one with both cationic and anionic moieties in its head group). The micellar samples behave as elastic gels at room temperature, as seen from the above photo where the sample holds its weight in the inverted vial. The sample also maintains its viscoelasticity even up to high temperatures (~ 90°C).

Citations: > 200 (Google Scholar)

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This paper, for the first time, enables one to easily create an aqueous fluid whose viscosity could be radically altered by shining light. The fluid contains surfactant molecules that self-assemble into long chains (wormlike micelles) initially. Irradiation with UV light alters the geometry of the surfactants, which makes them re-assemble into spherical micelles, causing a 10,000-fold drop in viscosity.

This work was highlighted in a variety of scientific media including Nature Materials and Materials Today.

Citations: > 200 (Google Scholar)

2006

35.    X. Huang, S. R. Raghavan, P. Terech, R. G. Weiss

34.    X. Wang,…J. H. Lee, S. R. Raghavan, D. S. English 

33.    T. S. Davies, A. M. Ketner, S. R. Raghavan

32.    S.-H. Tung, Y.-E. Huang, S. R. Raghavan

31.    D. R. Strachan, G. C. Kalur, S. R. Raghavan

Size-dependent diffusion in an aging colloidal glass.
Physical Review E 73, 041509 (2006)

30.    C. Zhu, J. H. Lee, S. R. Raghavan, G. F. Payne

29.    P. Elkouss, D. I. Bigio, M. D. Wetzel, S. R. Raghavan

28.    J. H. Lee, V. Agarwal, A. Bose, G. F. Payne, S. R. Raghavan

This paper reports an unusual phenomenon where the viscosity of a solution increases 1000-fold upon heating. It is shown to be due to a self-assembly transition in water from vesicles (i.e., discrete spheres) at low temperatures to ‘wormlike micelles’ (i.e., long, entangled chains) at high temperatures.

Citations: > 350 (Google Scholar)

This paper continues our study on the self-assembly of a biopolymer with hydrophobic side-chains when combined with vesicles. The remarkable result is that the biopolymer can sometimes convert unilamellar vesicles (i.e., hollow spheres with a single outer shell) to bilamellar vesicles (i.e., with two concentric shells). The latter are shown in the image above. Examples of bilamellar structures include the nucleus and mitochondria in our cells.

Self-assembly in oil (nonpolar organic liquids) has not been studied to the same extent as in water. This paper describes a new way to induce self-assembly of long chains (‘reverse wormlike micelles’) in oil: it involves mixing a lipid with bile salts. Both lipids and bile salts are biomolecules that are found in our body.

Citations: > 150 (Google Scholar)

2005

27.    G. C. Kalur, B. D. Frounfelker,…S. R. Raghavan

26.    A. F. Kostko,…M. A. Anisimov, D. Danino, S. R. Raghavan

25.    B. H. CiprianoS. R. Raghavan, P. M. McGuiggan

24.    P. A. Hassan,…S. K. Kulshreshtha, S. R. Raghavan

23.    G. C. Kalur and S. R. Raghavan

22.    X. Huang, P. Terech, S. R. Raghavan, R. G. Weiss

21.    J. H. Lee, J. P. Gustin, T. Chen, G. F. Payne, S. R. Raghavan

This paper documents an unusual effect: an increase in solution viscosity with temperature. The solutions contain a cationic surfactant and a naphthalene salt, which together form ‘wormlike micelles’. The micelles are shown to increase in length upon heating, which thereby causes the viscosity to rise.

Citations: > 150 (Google Scholar)

Cromolyn is an aromatic molecule that assembles into columns in water, which in turn align into nematic liquid crystals (LCs). These LCs reveal beautiful textures under polarized light microscopy. This paper shows that NaCl promotes the growth of the columns and thus widens the range of nematic behavior.

Citations: > 90 (Google Scholar)

This is the first study to show that ‘wormlike micelles’ (self-assembled chains) can be formed by anionic surfactants. The surfactant here is sodium oleate and it forms worms when combined with various salts.  Worms formed using triethylamine salts exhibit clouding, i.e., phase separation, upon heating.

Citations: > 150 (Google Scholar)

This paper shows that chains of a biopolymer with hydrophobic side-chains can connect vesicles into a network, i.e., into a ‘vesicle gel‘. The gel holds its weight in the inverted vial in the above image. The driving force for this self-assembly is hydrophobic interactions between the polymer and the vesicles.

Citations: > 150 (Google Scholar)

2004

20.    T. Kashiwagi,…B. H. Cipriano, S. R. Raghavan, J. R. Shields

19.    C. M. Aberg, T. Chen, A. Olumide, S. R. Raghavan, G. F. Payne

From U. Delaware Work (Postdoc)

18.    B. A. Schubert, N. J. Wagner, E. W. Kaler, S. R. Raghavan

17.    H.-P. Hentze, S. R. Raghavan, C. A. McKelvey, E. W. Kaler

Silica hollow spheres by templating of catanionic vesicles.
Langmuir 19, 1069 (2003)   (Citations > 300)

16.    S. R. Raghavan, G. Fritz, E. W. Kaler

15.    P. A. Hassan, S. R. Raghavan, E. W. Kaler

Microstructural changes in SDS micelles induced by hydrotropic salt.
Langmuir 18, 2543 (2002)   (Citations > 300)

14.    S. R. Raghavan, H. Edlund, E. W. Kaler

13.    S. R. Raghavan and E. W. Kaler

12.    R. D. Koehler, S. R. Raghavan, E. W. Kaler

Microstructure and dynamics of wormlike micelles formed by mixing cationic and anionic surfactants.
Journal of Physical Chem B 104, 11035 (2000)   (Citations > 300)

From NCSU Work (Ph.D.)

11.    B. S. Chiou, S. R. Raghavan, S. A. Khan

10.    J. S. Shay, S. R. Raghavan, S. A. Khan

  9.    S. R. Raghavan, H. J. Walls, S. A. Khan

  8.    S. R. Raghavan, J. Hou, G. L. Baker, S. A. Khan

  7.    T. A. Walker, S. R. Raghavan,…S. A. Khan, R. J. Spontak

  6.    R. J. English, S. R. Raghavan, R. D. Jenkins, S. A. Khan

  5.    J. Fan, S. R. Raghavan,…S. A. Khan, G. Baker, P. S. Fedkiw

  4.    S. R. Raghavan, M. W. Riley, P. S. Fedkiw, S. A. Khan

  3.    S. R. Raghavan and S. A. Khan

Shear-thickening response of fumed silica suspensions under steady and oscillatory shear.
Journal of Colloid & Interface Sci, 185, 57 (1997)  (Citations > 300)

  2.    S. R. Raghavan, L. A. Chen, C. McDowell, S. A. Khan

  1.    S. R. Raghavan and S. A. Khan

Shear-induced microstructural changes in flocculated suspensions of fumed silica.
Journal of Rheology 39, 1311 (1995)    (Citations > 150)

Review Articles and Book Chapters

  8.    N. Lamichhane,…W. D’Souza, C. Simone, S. R. Raghavan,…

  7.    S. R. Raghavan and Y. Feng

Wormlike micelles: Solutions, gels, or both?
in Wormlike Micelles, book published by RSC, p.9 (2017)

  6.    Y. Lan, M. Corradini, R. Weiss, S. R. Raghavan, M. Rogers

  5.    G. F. Payne,…S. R. Raghavan, J. N. Culver, W. E. Bentley

  4.    D. J. Durian and S. R. Raghavan

Making a frothy shampoo or beer.
Physics Today, 53, 62 (2010)

  2.    S. R. Raghavan and B. H. Cipriano

Gel formation: Phase diagrams using tabletop rheology and calorimetry.
in Molecular Gels, book published by Springer, p.233 (2005)

  1.    S. A. Khan, J. R. Royer, S. R. Raghavan

Rheology: Tools and Methods.
in Aviation Fuels with Improved Fire Safety, NAP, p.31 (1997)