Investigation of static and dynamic surface forces between soft-condensed matter

The physical and chemical properties of soft-condensed matter in nano-regime such as inorganic colloidal particles, soft vesicles and biological membranes are often very different from those of the bulk materials, displaying some unique properties that depend on their size, shape, composition and surface functional groups. The complex intermolecular and interparticle forces operating between various types of soft-condensed matter from biological to non-biological materials were identified and their roles in self- and directed-assembling processes were also studied in this dissertation.;The interactions between myelin membranes across aqueous medium were studied. Extracellular and cytoplasmic membranes of both healthy and diseased myelin were mimicked using Langmuir-Blodgett technique and their interaction forces were measured using the Surface Forces Apparatus technique. The measured adhesion forces of myelin membranes in the absence of myelin basic protein (MBP) appeared to be higher in the case of healthy cytoplasmic and extracellular sides compared to diseased ones which could be explained in terms of their lipid compositions. The force measurements with various amounts of myelin basic proteins were also performed and the results showed that a subtle charge balance between proteins and lipids could affect the water gap thickness and the inter-membrane adhesion. Phase transition behaviors on myelin membranes were also studied without and with proteins. The more tendencies to be phase-separated were found in diseased extracellular myelin membranes at physiological conditions. The amount of MBP also affected their phase transition behaviors clearly showing the existence of the maximum charge neutrality at a certain ratio between proteins and lipids in a similar way found in their normal force measurements.;The bilayer formation of zwitterionic dimyristoylphosphatidylcholine (DMPC) lipids on various glass substrates through the vesicle adsorption process was also investigated under different experimental conditions. While the type of substrates had no effects on the bilayer formation due to similar surface chemistries, temperature and concentration of lipids in the bulk led to significant changes on the formation of continuous bilayers. Simultaneous surface potential measurements and visualizations of the state of the substrate with different amounts of DMPC vesicles provided a more comprehensive picture of the bilayer formation using a miniature streaming potential apparatus which was newly developed.;The forces between two surfaces confining various surfactant-coated nanoparticles such as curved and straight nanowires and nanorods were studied in hydrocarbon solvents. The forces were exponentially repulsive when the surfactant layers were strongly bound to the nanoparticles in dry condition while roughly linear when the surfactant layers were detached from the nanoparticles due to the condensation of water bridges (in humid condition). Ordered nanostructured thin films could be produced by confinement and/or shearing processes. The frictional properties of nanoparticles appeared to be strongly affected by their geometries, sizes and the presence of trace amount of water in the system. Rod-shaped nanoparticles provided better lubrication properties than straight nanowires. The investigation of the forces between mica surfaces across room temperature ionic liquids (RTILs) was carried out. Their forces were exponentially repulsive at all distances while oscillatory at small separations. The Debye screening lengths from experiments were much longer than expected from traditional theories due to their size and molecular structures.