Journal of Surface Science and Technology

Kamla Rawat ¹

Affiliations
1 Special Centre for Nano Sciences, Jawaharlal Nehru University, New Delhi-110 067, IN

Abstract

We have studied the structural and thermo-mechanical properties of DNA-protein (gelatin A, GA) complex gels formed in imidazolium based ionic liquid solutions called ionogels generated has a result of first order phase transition from a complex coacervate. We probed the microscopic structure of these ionogels using Small Angle Neutron Scattering (SANS), differential scanning calorimetry (DSC) and rheological measurements. Data show that around 0.1% (w/v) GA concentration stiffening of DNA-GA complex takes place (optimum binding concentration). At higher temperature, the GA-DNA binding weakens and GA-GA interaction facilitates the reorganization of the material which on heating turns into ionosols. Ionosols when cooled to room temperature formed ionogels. The typical size of the complexes is a 150 nm (radius of gyration, R_g). SANS experiments indicate a mesh size, ξ≈3.8 ± 0.2 nm to these gels independent of protein concentration C_GA. Viscoelastic studies reveal that the storage and loss moduli (G' and G") values that are comparable, and the viscoelastic length ξ_el is typically double the mesh size of the network. It is found that these ionogels were associated with higher gel strength, and specific heat at optimum binding conditions. It is concluded that the DNA-gelatin complex ionogels comprise a unique class of designer soft material stable with respect to protein concentration change, higher gel strength and melting temperature compared to conventional gelatin gels.

Keywords

DNA, Gelatin, Ionogels, SANS, Rheology, Specific Heat.

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Nidhi Joshi ¹, Kamla Rawat ², Pratima R. Solanki ³, H. B. Bohidar ³

Affiliations
1 School of Physical Sciences, Jawaharlal Nehru University, New Delhi 110067, IN
2 Inter University Accelerator Centre (IUAC), New Delhi 110067, IN
3 Special Center for Nanosciences, Jawaharlal Nehru University, New Delhi 110067, IN

Abstract

Pectin is a branched polysaccharides found in the cell wall of the plants and commonly used in food industry as a gelling agent, emulsifier or stabilizer. The effect of calcium chloride on the gelation of pectin dispersions was studied using rheology and light scattering measurements. Addition of calcium induced the gel formation in pectin dispersions follows egg-box crosslink mechanism. Zeta potential measurements revealed the formation of cationic and anionic pectin gels on concentration of calcium. The cationic gels had higher rigidity compared to anionic gels. The sol-gel transition has been investigated for pectin-calcium system from the structure factor data which indicated cationic gels undergo transition earlier compared to anionic ones. The gelation time was determined from rheology and viscosity experiments and found to be less for cationic gels.

Keywords

Ca2+-pectin Gels, Egg-box Model, Gel Elastic Behaviour, Gel Stiffness, Gel Structure Development, Pectin, Rheology of Gels

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Jyotsana Pathak ¹, Kamla Rawat ², H. B. Bohidar ¹

Affiliations
1 School of Physical Sciences, Jawaharlal Nehru University, New Delhi - 110067, IN
2 Special Center for Nanosciences, Jawaharlal Nehru University, New Delhi - 110067, IN

Abstract

Herein, we report interaction between Gelatin B (GB) and Bovine Serum Albumin (BSA) which is mainly arising from surface selective patch binding occurring at their common pI (≈5.0 ± 0.5). The dispersion remained homogeneous with no indication of either complex formation or phase separation, but the dispersion turns gel-like phase over time. It was found that the initial tenuous network of GB provided a scaffold for network organization, the BSA molecules aggregated along the GB chains, and functioned as cross-linking agent, and more elastic gels were obtained for samples with higher GB content. We probe this dynamics in finer details and the gel phase displayed considerable change with aging time as the system moved from ergodic to non-ergodic state. GB-BSA based system exhibited anomalous relaxation in gels changing with aging time t_w at their common pI. At t_w = 0, the correlation function exhibited one relaxation mode due to the system residing deeply inside the ergodic phase and purely mirroring Brownian dynamics. After a characteristic waiting time, an additional mode (slow relaxation) appeared which was attributed to inter-chain interaction induced reorganization of entanglements.

Keywords

Dynamic Light Scattering, Ergodic–Non Ergodic Phase, Gel Structure Development, Mixed Protein Dispersion, Relaxation Dynamics in Gels.

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Pankaj Kumar Pandey ¹, Kamla Rawat ², H. B. Bohidar ¹

Affiliations
1 School of Physical Sciences, Jawaharlal Nehru University, New Delhi - 110067, IN
2 Department of Chemistry, School of Chemical and Life Sciences, Jamia Hamdard, Delhi - 110062, IN

Abstract

DNA ionogels prepared by adding 1-ethyl-3-methylimidazolium chloride on low energy gamma irradiated DNA solution samples reveal non-trivial self-assembly. Variations in secondary structure and low-frequency gel rigidity modulus G0 captured this unique hitherto unexplored features of these gels. Interestingly, at higher radiation dose (0 to 100 Gy) samples could partially lose their initial rigidity. Dynamic light scattering revels dose dependent relaxation dynamics corresponding to ergodicity breaking time. In particular, viscosity and rheology showed that the time of gelation t_gel, temperature of gelation T_gel and strength of gelation G₀ are gamma ray dose dependent. DNA Ionogel melting with temperature shows self-assembled characteristics of this biomaterial. Gelation kinetics of ionizing radiation treated DNA strands have been studied in literature.

Keywords

DNA Ionogel, Gelation, γ-Radiation, Ionizing Radiation.

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Rahul Ranjan ¹, Kamla Rawat ², H. B. Bohidar ¹

Affiliations
1 School of Physical Sciences, Jawaharlal Nehru University, New Delhi - 110067, IN
2 Department of Chemistry, School of Chemical and Life Sciences, Jamia Hamdard, New Delhi - 110062, IN

Abstract

TX-100 molecular hydrogels exhibited re-entrant melt-gel-sol phase transition driven solely by dilution, which sequentially altered the self-assembly of the micellar formations and their population was investigated through the monitoring of the physical parameters namely, solution viscosity, particle size histogram, ergodicity, and gel rigidity modulus. This phenomenon was noticed at 20° C in the TX-100 concentration region of 0.2 to 1.2 M much above the critical micellar concentration of 0.22 mM. The particle size histograms revealed the presence of spherical micelles (size »3 nm) in the solution ([TX-100] < 0.5 M) which formed entangled wormlike cylindrical micelles (apparent hydrodynamic radius » 50 nm) when (0.5 M< [TX-100] < 0.9 M) giving rise to a gel-like structure. Further increase in the TX-100 concentration increased the propensity of these wormlike cylindrical micelles that got randomly distributed creating a dense melt phase. Interestingly, we observed transition solely driven by dilution which defined complete re-entrant behavior at room temperature. These molecular gels could be created by dilution of the melt or concentration of the sol unlike in the polymer gels. Remarkably, this hitherto little known unique phenomenon was exhibited by a simple system of non-ionic surfactant solution. Thus, we have a hydration reversible gel at our disposal which has a special place in soft matter arena.

Keywords

Bulk Phenomena, Gelation Mechanism, Re-Entrant Phase Transition, Surfactant Gels, TX-100 Gel.

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