This project involves the study of several challenging sub-projects related to the equilibrium and transport properties of confined colloid-polymer mixtures (monolayers and channels). First, the PI will investigate experimentally by the Langmuir-Blodgett method the phase behavior of monolayers of colloid/polymer mixtures. The nanostructures of these monolayers will be determined by atomic force microscopy and Brewster angle microscopy. Secondly, a theoretical model will be developed based on that of McMillan to understand the phase transitions of these systems. Lastly, the PI will determine by florescence light microscopy the diffusion of polymer in channels as well as the diffusion of a pair of polymers in colloidal suspensions confined to narrow channels.
Intellectual Merit of the Proposed Activity
In the investigations of monolayers of colloid-polymer mixtures, a theory will be developed in order to describe the structure of the possible liquid-crystalline ordering of the polymers and the evidence garnered from the proposed experiments will be used to test the theoretical model. The theory will be modified if it fails to agree with the experiments, and the experimental parameters will be implemented in our theory. The details of experimental study of dynamics of polymer in channels will be investigated. The measurement resolution and uncertainty quantification are those of enhanced video fluorescent microscopy. The connection between theory and experiment for one-dimensional polymer diffusion will be studied. The theory of polymer diffusion in the presence of colloids in one-dimensional channels was developed in our previous NSF grant, and the coefficient of diffusivity was expressed in terms of the molecular parameters of the polymer, the size of the colloids, and the viscosity of the solvent. Since these quantities are directly measurable, our experiments will be directly connected to theory.
The problems that will be studied are challenging fundamental ones which require expertise in thermodynamics, statistical thermodynamics, theoretical and experimental physical chemistry and condensed matter physics. In particular, the experimental investigations of Langmuir-Blodgett monolayers of colloid-polymer mixtures will determine their phase transitions and shed light on unsolved problems related to depletion effects in confined geometries. The proposed activity is fundamental in nature, but it is inspired by and is beneficial to the numerous technological applications which involve self-assemblies of nano-particles and mixtures of colloids and polymers which are described in the proposal. These diverse fields of expertise required make it an interdisciplinary study not usually carried out by a single PI.
Broader Impacts Resulting from the Proposed Activity
In addition to the PI's graduate students, several of which have become professors at first-rate universities, a large number of undergraduate students will take part in the proposed activity, and several will make presentations at national and regional scientific meetings and become coauthors of publications, as has been the case under the previous NSF grant. Such integration and encouragement proves very effective in making undergraduate students of the PI, including many women, decide to go to graduate school in chemical engineering and in allied disciplines. The top undergraduate sophomore student at Rice University, a woman, has already expressed her interest in joining the group. The PI will continue to be involved in several outreach programs of Rice University, in which he discusses this proposed activity in understandable terms with middle and high school teachers and students, in predominantly African-American and Hispanic public schools of Houston, those most largely underrepresented in academia. The PI will pursue his efforts to convince them of the intimate bond between scientific and societal progress. The PI will also maintain the summer visits to his laboratory in which, during one week, several middle school students in the summer take part in research.
