@article { ISI:000303696200040, title = {Multiple topologies from glycopolypeptide-dendron conjugate self-assembly: nanorods, micelles, and organogels}, journal = {Journal of the American Chemical Society}, volume = {134}, number = {18}, year = {2012}, month = {APR}, pages = {7796-7802}, publisher = {AMER CHEMICAL SOC}, type = {Article}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

Glycopolypeptides (GPs) were synthesized by ring-opening polymerization of glycosylated N-carboxyanhydride monomer and attached to hydrophobic dendrons at one chain end by {\textquoteleft}{\textquoteleft}click{\textquoteright}{\textquoteright} reaction to obtain amphiphilic anisotropic macromolecules. We show that by varying polypeptide chain length and dendron generation, an organogel was obtained in dimethylsulfoxide, while nanorods and micellar aggregates were observed in aqueous solutions. Assemblies in water were characterized by electron microscopy and dye encapsulation. Secondary structure of the GP chain was shown to affect the morphology, whereas the chain length of the poly(ethylene glycol) linker between the GP and dendron did not alter rod-like assemblies. Bioactive surface chemistry of these assemblies displaying carbohydrate groups was demonstrated by interaction of mannose-functionalized nanorods with ConA.

}, issn = {0002-7863}, doi = {10.1021/ja300065f}, author = {Pati, Debasis and Kalva, Nagendra and Das, Soumen and Kumaraswamy, Guruswamy and Sen Gupta, Sayam and Ambade, Ashootosh V.} } @article {42995, title = {Molecular motifs for additives that retard PEO crystallization}, journal = {Polymer Engineering \& Science}, volume = {57}, year = {2017}, month = {AUG}, pages = {857-864}, type = {Article}, abstract = {

We investigate the influence of several bifunctional phenol additives (resorcinol: RES, hydroquinone: HYD, p-hydroxybenzoic acid: PHBA, and p-nitrophenol: PNP) on the crystallization of matrix polymer, polyethyleneoxide. We employ solid state Nuclear Magnetic Resonance spectroscopy (NMR), Differential Scanning Calorimetry (DSC), optical microscopy, and Small Angle X-ray Scattering (SAXS) to investigate crystallization of the additivated PEO and compare with Density Functional Theory (DFT) calculations of additive-PEO interactions. Additive-polymer interactions are a function of the functional groups on the additive. Temperature-dependent spherulitic growth rate measurements from optical microscopy and SAXS lamellar long spacings indicate a distinct trend in the effect of additives on PEO crystallization. Change in PEO crystallization is most pronounced with PNP, followed by PHBA and finally RES and HYD. This trend correlates qualitatively with the binding energies of additive-PEO interactions from DFT studies. Our results suggest that DFT calculations might be a useful screening tool to evaluate the influence of additives on polymer crystallization. POLYM. ENG. SCI., 2016. {\textcopyright} 2016 Society of Plastics Engineers

}, doi = {10.1002/pen.24462}, author = {Shrivastava, Sudhakar Dinesh and Eldho, Kavalakal Mathai and Rajamohanan, P. R. and Ajithkumar, Thalasseril G. and Vanka, Kumar and Kumaraswamy, Guruswamy} } @article {44590, title = {Modeling the universal viscoelastic response of polymer fibers}, journal = {Physical Review Materials}, volume = {2}, year = {2018}, month = {JUN}, pages = {062601}, abstract = {

Polymer fibers, including natural silk and synthetic fibers, exhibit universal viscoelastic response. On stretching below yield, they show logarithmic stress decay. On unloading fibers with a glassy amorphous phase, the stress recovers. A simple phenomenological model accurately describes data from independent mechanical experiments and provides insights into the micro structural origins of the fiber response. Counter to intuition, the model indicates that it is the crystalline regions, rather than the amorphous glass, that deform first on stretching fibers at high strain rates. On holding a stretched fiber, stress decays as a consequence of relaxations in amorphous regions. Finally, unloading the fiber transfers stress from the amorphous to crystalline regions resulting in stress recovery. Model parameters correlate well with the fiber microstructure. Crystal and amorphous moduli from the model match those from x-ray diffraction. Activation energies for the temperature dependence of the peak relaxation time are similar to those reported in the literature. Thus, a simple model that invokes only crystal-amorphous coexistence can successfully model the mechanical response of a wide variety of polymer fibers.

}, issn = {2475-9953}, doi = {10.1103/PhysRevMaterials.2.062601}, author = {Sharma, Aakash and Kumaraswamy, Guruswamy and Thakre, Shirish} } @article {46972, title = {Microstructural differences between Viscose and Lyocell revealed by in-situ studies of wet and dry fibers}, journal = {Cellulose}, volume = {27}, year = {2020}, month = {FEB}, pages = {1195-1206}, type = {Article}, abstract = {

Regenerated cellulose fibers manufactured using Lyocell and Viscose processes exhibit differences in their structural response to mechanical deformation. Here, we study the effect of stretching and stress relaxation on the orientation of crystal and amorphous phases. Our results show that on stretching, orientation in both crystal and amorphous phases increases linearly with strain, correlating with the increase in stress and with the stretching of the crystalline unit cell along the c-axis. On holding after stretching to a particular strain, the stress relaxes logarithmically in time, correlating with a decrease in the strain along the c-axis of the crystal unit cell. The stress relaxation is also correlated with a logarithmic increase in amorphous orientation, while crystalline orientation stays constant. We attribute the stress development during stretching to deformation of the crystal unit cell, while crystal reorientation in the fiber direction results in increase in the crystalline orientation parameter. On holding the fiber at a fixed total strain, the stress relaxes as strain is transferred from crystal to amorphous regions. Thus, the strain on the unit cell c-axis decreases and amorphous orientation increases. There are quantitative differences between the rate of increase in amorphous phase orientation during stress relaxation for Lyocell and Viscose fibers. For dry fibers, Lyocell shows a slower increase in orientation during stress relaxation. On wetting the fibers, their structural response changes qualitatively. We combine wide angle x ray diffraction and birefringence experiments with our model to infer that that on stretching the wet fiber, the crystalline phase is neither strained nor oriented. However, orientation develops in the amorphous phase. During stress relaxation in wet condition, Lyocell fibers shows a faster increase in amorphous orientation than Viscose fibers, in line with the comparison of relaxation time spectra for wet Viscose and Lyocell fibers. Graphic abstract

}, keywords = {birefringence, Crystal-amorphous orientation, In-situ WAXD, Regenerated cellulose}, issn = {0969-0239}, doi = {10.1007/s10570-019-02863-6}, author = {Sharma, Aakash and Thakre, Shirish and Kumaraswamy, Guruswamy} }