01953nas a2200181 4500008004100000022001400041245008300055210006900138260007100207300001400278490000800292520126200300100002501562700002701587700001701614700002801631856011201659 2009 eng d a1520-610600aSelf-assembly of silica particles in a nonionic surfactant hexagonal mesophase0 aSelfassembly of silica particles in a nonionic surfactant hexago a1155 16TH ST, NW, WASHINGTON, DC 20036 USAbAMER CHEMICAL SOCcMAR a3423-34300 v1133 a

We investigate the process of self-assembly, and the resultant structures in composites of silica particles with a hexagonal mesophase of a nonionic surfactant and water. We report a systematic transition in behavior when the particle size is increased relative to the characteristic mesophase spacing. Water dispersible cage-like silsesquioxanes that are molecular analogues of silica particles and are smaller than the mesophase spacing swell the space between the surfactant cylinders. Silica particles comparable to the characteristic hexagonal spacing partition into the hexagonal phase and into strandlike particulate aggregates. Even larger particles phase separate from the hexagonal phase to form particulate strands that organize with a mesh size comparable to the wavelength of visible light. This self-assembly is reversible and the particles disperse by breaking up the aggregates on heating the composite into the isotropic phase. On cooling from the isotropic phase into the hexagonal, the particles are expelled from the growing hexagonal domains and finally impinge to form strandlike aggregates. Unusually, the isotropization temperature is increased in the composites as the particles nucleate the formation of the hexagonal phase.

1 aSharma, Kamendra, P.1 aKumaraswamy, Guruswamy1 aLy, Isabelle1 aMondain-Monval, Olivier uhttps://library.ncl.res.in/content/self-assembly-silica-particles-nonionic-surfactant-hexagonal-mesophase-001922nas a2200169 4500008004100000022001400041245011400055210006900169260007100238300001600309490000800325520121500333100002501548700002101573700002701594856013101621 2010 eng d a1520-610600aAdsorption of nonionic surfactant on silica nanoparticles: structure and resultant interparticle interactions0 aAdsorption of nonionic surfactant on silica nanoparticles struct a1155 16TH ST, NW, WASHINGTON, DC 20036 USAbAMER CHEMICAL SOCcSEP a10986-109940 v1143 a

Addition of nonionic surfactant, C(12)E(9), to an aqueous dispersion of charge stabilized silica nanoparticles renders particle aggregation reversible. In contrast, aggregation of the same silica particles in aqueous solutions is irreversible. We use a combination of small-angle X-ray scattering (SAXS) and contrast matching small-angle neutron scattering (SANS) to investigate interparticle interactions and microstructure in dispersions of silica particles in aqueous nonionic surfactant solutions. We show that the silica particles interact through a screened Coulombic interaction in aqueous dispersions; interestingly, this interparticle interaction is hard-sphere-like in surfactant solutions. In surfactant solutions, we show that the final surfactant-particle structure can be modeled as 14 micelles adsorbed (on average) on the surface of each silica particle. This gives rise to the short-range interparticle repulsion that makes particle aggregation reversible, and results in the hard sphere interparticle interaction potential. Finally, we show that adsorption of polyethylene imine on the surface of the silica particles prevents adsorption of surfactant micelles on the particle surface.

1 aSharma, Kamendra, P.1 aAswal, Vinod, K.1 aKumaraswamy, Guruswamy uhttps://library.ncl.res.in/content/adsorption-nonionic-surfactant-silica-nanoparticles-structure-and-resultant-interparticle-002591nas a2200229 4500008004100000022001400041245007700055210006900132260007100201300001400272490000700286520177200293100001702065700002502082700001802107700002202125700002402147700003202171700002502203700002702228856010602255 2010 eng d a0024-929700aVolume transition of PNIPAM in a nonionic surfactant hexagonal mesophase0 aVolume transition of PNIPAM in a nonionic surfactant hexagonal m a1155 16TH ST, NW, WASHINGTON, DC 20036 USAbAMER CHEMICAL SOCcMAY a4782-47900 v433 a

We investigate the volume transition of a thermoresponsive polymer, poly(N-isopropylacrylamide), PNIPAM, in the presence of an aqueous solution of nonionic surfactant, C(12)E(9). We combine turbidimetry with optical microscopy, NMR, and SAXS to follow the volume transition of the PNIPAM and the H(1)-isotropic transition of the surfactant/water system. Nonionic surfactants such as C(12)E(9) are known to interact weakly with PNIPAM. Accordingly, we show that there is only a small change in the volume transition temperature for the PNIPAM in isotropic micellar solutions of C(12)E(9), even for relatively high concentrations of C(12)E(9). Interestingly, once the surfactant forms an H(1) phase, there is a dramatic decrease in the coil globule transition onset temperature. We believe that this behavior results from a competition between C(12)E(9) in the H(1) phase, and PNIPAM to associate with water. When PNIPAM in the H(1) phase is cooled to low enough temperatures so as to be in the coil state, it locally disturbs the hexagonal phase ordering. Thus, we show that for PNIPAM in a weakly interacting surfactant matrix, it is the phase behavior of the matrix rather than the matrix chemistry that governs the coil globule transition. Finally, we show that in a PNIPAM copolymer with a higher LCST we observe an interesting sequence of transitions in the surfactant phase: on cooling from a high temperature free-blowing turbid globular state (similar to 75 degrees C), we enter a free-flowing translucent coil phase (similar to 47 degrees C), then a turbid gel (similar to 25 degrees C) where the copolymer is collapsed in the HI phase, and finally a low-temperature clear gel (similar to 5 degrees C) where the copolymer is in the expanded coil state.

1 aJijo, V., J.1 aSharma, Kamendra, P.1 aMathew, Renny1 aKamble, Samruddhi1 aRajamohanan, P., R.1 aAjithkumar, Thalasseril, G.1 aBadiger, Manohar, V.1 aKumaraswamy, Guruswamy uhttps://library.ncl.res.in/content/volume-transition-pnipam-nonionic-surfactant-hexagonal-mesophase-002631nas a2200217 4500008004100000022001400041245011400055210006900169260007100238300001400309490000800323520179600331100002502127700003002152700002202182700002102204700002402225700001502249700002702264856012202291 2011 eng d a1520-610600aAssembly of polyethyleneimine in the hexagonal mesophase of nonionic surfactant: effect of pH and temperature0 aAssembly of polyethyleneimine in the hexagonal mesophase of noni a1155 16TH ST, NW, WASHINGTON, DC 20036 USAbAMER CHEMICAL SOCcJUL a9059-90690 v1153 a

We investigate the dispersion of a pH responsive polymer, polyethyleneimine, PEI, in a hexagonal (H(1)) mesophase of a nonionic surfactant, C(12)E(9), and water, at pH ranging from basic (pH = 12.8) to acidic (pH = 1). While the C(12)E(9)/H(2)O phase behavior is independent of pH, we demonstrate that, in the PEI/C(12)E(9)/H(2)O system, changing the pH influences PEI-C(12)E(9) interactions, and thus, influences the isotropic-H(1) phase transition. With decrease in pH, there is increasing protonation of the PEI chain, and consequently, the chain extends. We show, using a combination of SAXs, optical microscopy and visual experiments, that the inclusion of PEI in a 1:1 surfactant water mixture, lowers the hexagonal-isotropic transition temperature, T. At higher pH = 12.8 T(HI) shows a pronounced decrease from SO to 13 degrees C on addition of PEI, and the PEI/C(12)E(9)/H(2)O system forms a transparent gel. At pH = 1, we observe qualitatively different behavior and an opaque gel forms below T(HI)= 25 degrees C. The isotropic-H(1) transition, in turn, influences the phase separation of PEI chains from the C(12)E(9)/H(2)O system. 2D NMR ROESY data provides evidence that there are strong surfactant PEI interactions at high pH that significantly reduce at lower pH. The NMR data is in accord with molecular dynamics simulations that show that surfactants strongly aggregate with unprotonated PEI chains, but not with fully protonated chains; thus, in this system, the pH controls a cascade of microstructural organization: increasing pH decreases chain protonation and increases polymer-surfactant interactions, resulting in suppression of the isotropic-H(1) transition to lower temperatures, thus, influencing the phase separation of PEI from the surfactant/water system.

1 aSharma, Kamendra, P.1 aChoudhury, Chandan, Kumar1 aSrivastava, Sonal1 aDavis, Hilda, C.1 aRajamohanan, P., R.1 aRoy, Sudip1 aKumaraswamy, Guruswamy uhttps://library.ncl.res.in/content/assembly-polyethyleneimine-hexagonal-mesophase-nonionic-surfactant-effect-ph-and-001917nas a2200241 4500008004100000022001400041245014500055210006900200260007100269300001400340490000700354520100900361653001401370653001601384653001701400653001801417653001501435100002501450700002301475700002201498700002701520856012801547 2011 eng d a0897-475600aSelf-standing three-dimensional networks of nanoparticles with controllable morphology by dynamic templating of surfactant hexagonal domains0 aSelfstanding threedimensional networks of nanoparticles with con a1155 16TH ST, NW, WASHINGTON, DC 20036 USAbAMER CHEMICAL SOCcAPR a1448-14550 v233 a

Assembly of nanoparticles into free-standing three-dimensional networks has implications for a wide range of applications. We show that dynamic templating of surfactant hexagonal domains is a facile technique to organize nanoparticles into a network of particulate strands. Dispersed particles (> 10 nm), independent of particle chemistry, assemble into networks, when the surfactant matrix cools into the hexagonal phase. We demonstrate assembly of inorganic, polymeric, and protein nanoparticles into networks. Where particle assembly is reversible, particles are coated with polymers that are subsequently cross-linked to stabilize the networks after surfactant removal. This technique involves near ambient temperatures and a benign water wash for template removal. The network mesh size can be varied from submicrometers to tens of micrometers by controlling the cooling rate. Particle networks can be flow-oriented prior to cross-linking, and interpenetrating networks can also be formed.

10ahexagonal10amacroporous10ananoparticle10aself assembly10asurfactant1 aSharma, Kamendra, P.1 aGanai, Anal, Kumar1 aGupta, Sayam, Sen1 aKumaraswamy, Guruswamy uhttps://library.ncl.res.in/content/self-standing-three-dimensional-networks-nanoparticles-controllable-morphology-dynamic-001259nas a2200205 4500008004100000022001400041245011400055210006900169260011000238300001400348490000700362520041800369100002300787700001900810700002500829700002100854700002700875700002200902856012900924 2012 eng d a1359-734500aSynthesis of functional hybrid silica scaffolds with controllable hierarchical porosity by dynamic templating0 aSynthesis of functional hybrid silica scaffolds with controllabl aTHOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLANDbROYAL SOC CHEMISTRYcMAR a5292-52940 v483 a

We report a facile one-pot synthesis of hierarchically porous scaffolds, with independent control over nanoparticle mesoporosity and scaffold macroporosity. Our technique combines the chemistry of mesoporous silica nanoparticles with the control afforded by dynamic templating of surfactant mesophases. These materials are readily functionalizable and allow controllable spatial variation in macroporosity.

1 aGanai, Anal, Kumar1 aKumari, Sushma1 aSharma, Kamendra, P.1 aPanda, Chakadola1 aKumaraswamy, Guruswamy1 aGupta, Sayam, Sen uhttps://library.ncl.res.in/content/synthesis-functional-hybrid-silica-scaffolds-controllable-hierarchical-porosity-dynamic-001822nas a2200193 4500008004100000022001400041245011000055210006900165260007100234300001600305490000800321520104600329100002501375700002301400700001701423700003001440700002701470856013101497 2013 eng d a1520-610600aExclusion from hexagonal mesophase surfactant domains drives end-to-end enchainment of rod-like particles0 aExclusion from hexagonal mesophase surfactant domains drives end a1155 16TH ST, NW, WASHINGTON, DC 20036 USAbAMER CHEMICAL SOCcOCT a12661-126680 v1173 a

Anisotropic rod-like particles assemble end-to-end when the surfactant/water matrix in which they are dispersed is cooled from the isotropic to the lyotropic hexagonal phase. We demonstrate the formation of such end-to-end assemblies for gold nanorods, which are tens of nanometers in size, as well as for micrometer-sized ellipsoidal polystyrene particles. In both cases, the particles are well-dispersed in the low-viscosity surfactant/water phase above the isotropic-H-1 transition temperature. On cooling into the H-1 phase, mesophase domains form and the particles are expelled to the isotropic phase. As the H-1 domains grow and finally impinge, the particles are localized at the domain boundaries where they reorient and assemble end-to-end. Remarkably, we observe the formation of end-to-end assemblies of gold nanorods even for volume fractions as low as 2 x 10(-6) in the initially dispersed state. The extent of particle ``enchainment'' increases with the particle concentration and with the aspect ratio of the particles.

1 aSharma, Kamendra, P.1 aGanai, Anal, Kumar1 aSen, Debasis1 aPrasad, Bhagavatula L. V.1 aKumaraswamy, Guruswamy uhttps://library.ncl.res.in/content/exclusion-hexagonal-mesophase-surfactant-domains-drives-end-end-enchainment-rod-particles-002466nas a2200253 4500008004100000022001400041245011700055210006900172260000800241300001600249490000600265520162400271653001501895653001901910653002401929653001601953653001701969100001501986700002102001700002002022700001702042700002502059856012802084 2022 eng d a2637-610500aViscoelastic liquid from regenerated silk fibroin in the silk i conformation: a writeable and shapeable material0 aViscoelastic liquid from regenerated silk fibroin in the silk i  cJUN a4699–47080 v43 a

Regenerated silk fibroin (RSF) has acquired enormous attention because of its exceptional toughness, strength, and biocompatible nature. These properties make RSF a potential candidate for the fabrication of different types of materials. However, processing even a dilute aqueous solution of RSF leads to a conformational transformation from a random coil/helix-rich (silk I) to a beta-sheetrich (silk II) state. As a consequence, RSF tends to form aggregates and loses its toughness. Working in a direction to address this problem, an aqueous solution of regenerated silk fibroin has been modified with a dual layer of polyethylenimine (PEI) and a PEG-based polymer surfactant (PS). Upon freeze-drying, the RSF-polymer complex forms a solvent-free RSF bioconjugate system and exhibits a soft solid to liquid melting transition at similar to 45 degrees C. The sequential modification with PEI and PS preserves the native-like random coil conformation of RSF up to at least 8 months of storage by not allowing interchain interactions that can lead to aggregation. Rheological and small-angle X-ray scattering measurements show that the solvent-free system is viscoelastic and exhibits a higher order microstructure mediated by the packing of the PS chains, respectively. Temperature-dependent soft solid-liquid-like dual behavior offers applications in injection-based writing, compression molding, and shaping RSF bioconjugates into various types of geometries. Furthermore, the mechanical properties of the RSF bioconjugate system can be modulated by crosslinking with glutaraldehyde vapor at 50 degrees C.

10aRSF liquid10aRSF soft solid10asilk I conformation10asilk liquid10aviscoelastic1 aKumar, Raj1 aJoseph, Emmanuel1 aChaudhari, Atul1 aNisal, Anuya1 aSharma, Kamendra, P. uhttps://library.ncl.res.in/content/viscoelastic-liquid-regenerated-silk-fibroin-silk-i-conformation-writeable-and-shapeable