Some excursions in the world of stimuli-responsive polymeric gels

Stimuli-responsive polymeric gels are attracting increasing attention due to their great potential as smart materials. Some of the recent work in the area of science and applications of these materials, including from our own school at NCL, is described. The quantitative basis for volume transltion in the gels is first presented. Our recent findlugs on deformation-dependent swelling as well as certain aspects of microdynamics in gels studied through NMR have been highlighted. Specific appilcatlons based on this fundamental understandmg have been described. These include the development of a macromolecular separation technique based on swelling/collaping gels. The basis for diffusion modulation of gels to switch from Fickian to non-Fickian dlifusion has been presented. A practical application of such diffusion modulation in sustained-release ystrms is described. Diverse applications exploiting the stimuli-responsive ability of gels in areas such as sensors, soft actuators, artificial muscles, intelligent sponges, etc., are finally presented

Intellectual property rights and the Third World

Issues of generation, protection and exploitation of intellectual property (IP) are assuming increasing importance. The new IP regimes will have wide ranging socio-economic, technological and political impact. As per the obligations under the Traderelated Aspects of Intellectual Property Systems (TRIPS), all the members of World Trade Organization (WTO) are supposed to implement national systems of intellectual property rights following an agreed set of minimum standards. However, there is an increasing feeling that harmonization is demanded from those that are not equal, either economically or institutionally. The major concerns of the Third World about such harmonization and the new challenge it faces in diverse areas of intellectual property protection are discussed and some suggestions about the way ahead are made. The discussion includes the need for a fair play in technology transfer, creation of 'favourable economics' of essential medicines from the point of view of the Third World, protection of traditional knowledge, etc. The creation of Traditional Knowledge Digital Library (an essentially Indian initiative) and linking it to the International Patent Classification System (IPC) through a Traditional Knowledge Resource Classification System is an important conceptual step forward. The possible models for material transfer and benefit sharing when products are created based on community knowledge are also discussed. Other discussions include the challenge of bridging the divide between the Third World and other developed nations, with special emphasis on intellectual property information sharing, capacity building with creation of appropriate physical and intellectual infrastructure and awareness building. It is argued that the Third World should negotiate a new 'TRIPS plus' which means 'TRIPS plus equity and ethics'

Fun and joy of Science: learning from Anomalies and Discontinuities

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On slip effect in free coating of non-Newtonian fluids

The failure of the current theories to predict the coating thickness of non-Newtonian fluids in free coating operations is shown to be a result of the effective slip at the moving rigid surface being coated. This slip phenomenon is a consequence of stress induced diffusion occurring in flow of structured liquids in non-homogeneous flow fields. Literature data have been analysed to substantiate the slip hypothesis proposed in this work. The experimentally observed coating thickness is shown to lie between an upper bound, which is estimated by a no-slip condition for homogeneous solution and a lower bound, which is estimated by using solvent properties. Some design considerations have been provided, which will serve as useful guidelines for estimating coating thickness in industrial practice

Longitudinal dispersion in rectilinear flow of dilute polymeric liquids: likely role of stress-induced migration

The likely role of stress-induced macromolecular migration in interpreting certain anomalous observations in longitudinal dispersion is discussed. In majority of the cases considered, the migration phenomenon affords an explanation for such behaviour, although in some instances, the operational regime for the dispersion process can itself explain the anomalies. In those cases, where stress-induced migration could be a contributory factor, a semi-quantitative discussion based on our current understanding of the phenomenon is presented. Such a development, though rather simplistic in nature, enables (at least) a semi-quantitative elucidation of the pertinent variables which may affect the longitudinal dispersion processes involving polymeric media

Mass transfer augmentation due to wall slip in haemodialysers

The inadequacy of the current theories to accurately predict the haemodialyser performance is shown to be a result of the effective slip at the membrane surface. This slip phenomenon, manifested by the Fahraeus-Lindqvist effect is peculiar to (heterogeneous) blood flow. Literature data have been analyzed to substantiate the slip hypothesis proposed in this work. Both the theoretical analysis and the experimental observations indicate that slip enhances haemodialyser performance. Some design considerations have been provided, which will account for the beneficial effect of wall slip in practical haemodialyser operations

Role of thermodynamic and kinetic factors in polymer dissolution in mixed solvents+

A model for polymer dissolution in mixed solvents has been developed with the purpose of explaining the hitherto unexplained maximum in the dissolution rate with the solvent composition. The variation of the interface concentration of both the solvents and the dissolution rate with the composition of the non-solvent in the dissolution medium is predicted. The model predicts an increase in dissolution rate with an increase in low molecular weight non-solvent content of the dissolution medium. However, further increase in the non-solvent content, decreases the dissolution rate. The relative role of kinetic and thermodynamic quality of the solvent is shown to be the reason for this unusual behaviour. The model also predicts reduction in swelling with an increase in non-solvent content of the dissolution medium. The implications of the work in designing mixed solvent systems for microlithography to meet the goal of maximum dissolution rate with minimum swelling are discussed

Prediction of the slope discontinuity in stress-strain behaviour of polymeric composites with spherical inclusions

The estimation of the point of discontinuity in the slope of stress-strain curves (commonly referred to as "knee") generally observed with composite polymeric materials could be an important problem for the specific application of the composite items. In this work, we have used the results from classical elasticity theory to calculate the residual thermal stresses and proposed simplifying assumptions to calculate a "lower bound" on the applied stress value at which the "knee" can occur. The theoretical predictions have been then compared with the experimental data on various polymeric composites containing glass beads and the agreement is found to be very sound. The proposed equation can be reliably used in engineering design

On the role of stress-induced migration on time-dependent terminal velocities of falling spheres

There is experimental evidence to suggest that even under steady-state conditions the velocity of solid spheres or bubbles moving through viscoelastic fluids can become time dependent. One of the possible explanations offered for interpreting this phenomenon has been the generation of a polymer depleted layer in the line of passage Of the particles, which disappears due to the counterbalancing effect of molecular diffusion in the long range. We have done some careful experiments and measured these concentrations to show that no such depletion layers are formed. Alternative explanations of the phenomenon have been examined and the importance of the possible effects of microstructures generated through temporary associations has been emphasised

Unified altered free volume state model for transport phenomena in polymeric media

An Altered Free Volume State (AFVS) model has been proposed for analysing and correlating a variety of transport phenomena in polymeric media. The key concept is the calculation of the alteration of the free volume state of the parent medium with respect to a carefully defined reference state. This approach enables the prediction of the influence of alteration of many variables including the changes in the physico-chemical structural attributes of the polymeric systems on a surprisingly large variety of transport phenomena. The successful application of this unified model has been demonstrated by analysing exhaustive experimental data