Adsorption of poly acrylic acid onto the surface of calcite: an experimental and simulation study.

Macromolecular binding to minerals is of great importance in the formation of biofilms, and carboxylate functional groups have been found to play a pivotal role in the functioning of these macromolecules. Here we present both fluorescence time-resolved anisotropy measurements and simulation data on the conformational behaviour and binding of a poly acrylic acid polymer. In solution the polymer exhibits a pH dependent behaviour, with a coiled conformation at a low pH and extended conformation at higher pH values. The polymer is readily adsorbed on the surface of calcite, preferring to bind in an extended conformation, with the strength of the adsorption dependent on the pH and presence of counter ions. We discuss the reasons why the calculated adsorption free energy differs from that obtained from a Langmuir isotherm analysis, showing that they refer to different quantities. The enhanced binding of the extended conformations shows the importance of flexibility in the binding of macromolecules.

Molecular-level surface structure from nonlinear vibrational spectroscopy combined with simulations.

Vibrational sum-frequency generation spectroscopy is valued for its ability to selectively probe molecules at a variety of interfaces without the use of extrinsic chromophores. The spectra contain valuable information regarding the molecular structure and the interfacial environment through the observation of vibrational resonances associated with specific moieties. Chemical information is obtained by close inspection of the frequencies of these bands and the amplitude of the response under conditions of different beam polarizations. Such sensitivity motivates the development of techniques that can provide structural details. We illustrate several approaches by which various types of calculations and molecular simulations may be used to enhance the sought structural interpretation of experimental data. By applying these techniques to the adsorbate molecules, interfacial water, and the substrate surfaces themselves, we are able to achieve a holistic picture of the adsorption environment.

Combined Stokes vector and Mueller matrix polarimetry for materials characterization.

A robust way of measuring the optical properties of any material is to interrogate it with light of different polarizations. The 16-element Mueller matrix provides the most complete description of the optical properties of a sample based on its ability to alter the polarization state of transmitted or reflected light. This is valuable for ordered and isotropic materials alike. Similarly, the 4-element Stokes vector is the most complete description of the polarization of a light beam, including any depolarization effects. While the Mueller matrix offers the most chemical and physical insight, the Stokes vectors are easier to obtain, and there are more schemes for measuring them quickly in situations where time resolution is important. We describe a method where any Stokes polarimeter may be adapted to obtain Mueller matrices and discuss various approaches for achieving better time resolution.