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Fluorescence spectroscopy on a series of aqueous solutions of poly(acrylic acid) containing a luminescent label showed that polymers with molar mass, Mn < 16.5 kDa did not exhibit a pH responsive conformational change, which is typical of higher molar mass poly(acrylic acid). Below this molar mass, polymers remained in an extended conformation, regardless of pH. Above this molar mass, a pH-dependent conformational change was observed. Diffusion-ordered nuclear magnetic resonance spectroscopy confirmed that low molar mass polymers did not undergo a conformational transition, although large molar mass polymers did exhibit pH-dependent diffusion.

Blends of conjugated polymers are frequently used as the active semiconducting layer in light-emitting diodes and photovoltaic devices. Here we report the use of scanning near-field optical microscopy, scanning force microscopy and nuclear-reaction analysis to study the structure of a thin film of a phase-separated blend of two conjugated polymers prepared by spin-casting. We show that in addition to the well-known micrometre-scale phase-separated morphology of the blend, one of the polymers preferentially wets the surface and forms a 10-nm-thick, partially crystallized wetting layer. Using near-field microscopy we identify unexpected changes in the fluorescence emission from the blend that occurs in a 300-nm-wide band located at the interface between the different phase-separated domains. Our measurements provide an insight into the complex structure of phase-separated conjugated-polymer thin films. Characterizing and controlling the properties of the interfaces in such films will be critical in the further development of efficient optoelectronic devices.

Poly(methacrylic acid) (PMAA) undergoes a conformational transition between pH 4 and 6 from a hypercoiled structure to a water-swollen state. There has been much speculation as to the exact nature and driving force of the transition. In this paper, we present a comprehensive investigation of the conformational switch of PMAA using techniques which report on various length scales:  fluorescence energy transfer experiments provide unique information on the nanometer length scale while dynamic light scattering (DLS) offers an insight into longer range interactions involved in the transition. Fluorescence energy transfer measurements demonstrate that PMAA undergoes subtle molecular rearrangements between pH 2 and 5 as short-range hydrophobic interactions between methyl groups are broken down by increasing concentrations of mutually repulsive carboxylate anions. Although such rearrangements have been proposed to account for the pH behavior of PMAA, we reveal them experimentally using techniques sensitive to nanoscale events. Fluorescence lifetime measurements indicate a rather complex structure within the collapsed chain, and time-resolved anisotropy measurements also demonstrate the importance of intramolecular interactions at low pH. A critical point, at pH 5.7, is reached in terms of the carboxylate anion concentration where a macroscopic transition occurs (as monitored by DLS):  the concentration of carboxylate anions is such that repulsive interactions dominate, and a switch occurs from a compact, globular form to an expanded state when neutralization of the PMAA is complete. We conclude that small-scale rearrangements in structure occur between pH 2 and 5, rather than a large-scale expansion, which is then followed by a macroscopic change in dimension at the neutralization point. Our results comprehensively describe the conformational behavior of PMAA and reconcile, to some extent, previous conflicting experimental data in the literature.

We have used optical microscopy and scanning force microscopy to study the dewetting of polystyrene from poly(methyl methacrylate) on silicon substrates as a function of film thickness. We have performed measurements for bilayers with a lower layer more viscous than the upper layer, as well as for the opposite situation. For a solidlike (highly viscous) lower layer, the dewetting speed is constant and independent of the thickness of the polystyrene film. However, for a liquidlike lower layer, the radius of the dewetted holes grows as t 2/3 , where t is the annealing time, and depends on the thickness of both layers. The absolute values of the dewetting speed are in reasonable agreement with theoretical predictions.

We study the wetting behaviour of thin polystyrene (PS) films on regularly corrugated silicon substrates. Below a critical film thickness the PS films are unstable and dewet the substrates. The dewetting process leads to the formation of nanoscopic PS channels filling the grooves of the corrugated substrates. Films thicker than the critical thickness appear stable and follow the underlying corrugation pattern. The critical thickness is found to scale with the radius of gyration of the unperturbed polymer chains.

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Progress in the development of generic molecular devices based on responsive polymers is discussed. Characterisation of specially synthesised polyelectrolyte gels, "grafted from" brushes and triblock copolymers is reported. A Landolt pH-oscillator, based on bromate/ sulfite/ferrocyanide, with a room temperature period of 20 min and a range of 3.1 < pH < 7.0, has been used to drive periodic oscillations in volume in a pH responsive hydrogel. The gel is coupled to the reaction and changes volume by a factor of at least 6. A continuously stirred, constant volume, tank reactor was set-up on an optical microscope and the reaction pH and gel size monitored. The cyclic force generation of this system has been measured directly in a modified JKR experiment. The responsive nature of polyelectrolyte brushes, grown by surface initiated ATRP, have been characterised by scanning force microscopy, neutron reflectometry and single molecule force measurements. Triblock copolymers, based on hydrophobic end-blocks and either polyacid or polybase mid-block, have been used to produce polymer gels where the deformation of the molecules can be followed directly by SAXS and a correlation between molecular shape change and macroscopic deformation has been established. The three systems studied allow both the macroscopic and a molecular response to be investigated independently for the crosslinked gels and the brushes. The triblock copolymers demonstrate that the individual response of the polyelectrolyte molecules scale-up to give the macroscopic response of the system in an oscillating chemical reaction.