This contribution offers a comprehensive understanding of the factors that govern the morphologies of Langmuir-Blodgett (LB) monolayers of amphiphilic diblock copolymers (BCs). This is achieved by a detailed investigation of a wide range of polystyrene-poly(4-vinyl pyridine) (PS-P4VP) block copolymers, in contrast to much more limited ranges in previous studies. Parameters that are varied include the block ratios (mainly for similar total molecular weights, occasionally other total molecular weights), the presence or not of 3-n-pentadecylphenol (PDP, usually equimolar with VP, with which it hydrogen bonds), the spreading solution concentration ("low" and "high"), and the LB technique (standard vs "solvent-assisted"). Our observations are compared with previously published results on other amphiphilic diblock copolymers, which had given rise to contradictory interpretations of morphology formation. Based on the accumulated results, we re-establish early literature conclusions that three main categories of LB block copolymer morphologies are obtained depending on the block ratio, termed planar, strand, and dot regimes. The block composition boundaries in terms of mol % block content are shown to be similar for all BCs having alkyl chain substituents on the hydrophilic block (such as PS-P4VP/PDP) and are shifted to higher values for BCs with no alkyl chain substituents (such as PS-P4VP). This is attributed to the higher surface area per repeat unit of the hydrophilic block monolayer on the water surface for the former, as supported by the onset and limiting areas of the Langmuir isotherms for the BCs in the dot regime. 2D phase diagrams are discussed in terms of relative effective surface areas of the two blocks. We identify and discuss how kinetic effects on morphology formation, which have been highlighted in more recent literature, are superposed on the compositional effects. The kinetic effects are shown to depend on the morphology regime, most strongly influencing the strand and, especially, planar regimes, where they give rise to a diversity of specific structures. Besides film dewetting mechanisms, which are different when occurring in structured versus unstructured films (the latter previously discussed in the literature), kinetic influences are discussed in terms of chain association dynamics leading to depletion effects that impact on growing aggregates. These depletion effects particularly manifest themselves in more dilute spreading solutions, with higher molecular weight polymers, and in composition regimes characterized by equilibrium degrees of aggregation that are effectively infinite. It is by understanding these various kinetic influences that the diversity of structures can be classified by the three main composition-dependent regimes.

We describe a simple manipulation of an asymmetric diblock copolymer, polystyrene-b-poly(4-vinylpyridine), mixed with 3-pentadecylphenol that generates a dense network of interconnected nanostrands at the air/water interface. This morphology is obtained by compression of the solution immediately after spreading, contrasting with the dot-and-planar morphology obtained by the conventional method, and is attributed to the presence of the solvent that confers sufficient mobility to the system to enable reorganization in response to increased surface pressure. This procedure thus adds a facile yet effective tool for controlling pattern formation at the air/water interface.

Time-resolved hot-stage transmission optical microscopy is used to characterize the nucleation and growth kinetics of amorphous GeTe thin-film crystallization. This technique provides experimental measurements of the fraction crystallized, the number of crystallites, and the crystallite size as a function of annealing time and temperature. The fraction-crystallized data are modelled using the Johnson-Mehl-Avrami formalism to give an Avrami exponent of 4, consistent with previous measurements via time-resolved reflection/transmission methods. Microstructural measurements provide sufficient data to deconvolute the individual contributions of nucleation and growth to this exponent. This work shows that crystallization of these films proceeds by nucleation at an increasing rate due to transient effects with isotropic two-dimensional growth in the film plane. 0 1995 American Institute of Physics.

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2,2,6,6-Tetramethyl-4-piperidinol (TMP) crystal is a very important intermediate in organic synthesis. To obtain an improved crystallization yield and desirable crystal-size characteristics, several commonly used organic solvents were investigated to determine the solubility of TMP using a gravimetric method. An ethanol solvent and a cooling crystallization method were chosen to obtain an improved theroretical yield. The cooling crystallization process of TMP in the ethanol solution was further optimized to crystallize larger crystals with a narrow crystal-size distribution using an orthogonal array design. Final TMP crystals with an average diameter of 1110 μm and a diameter span of 0.715 were obtained under laboratory conditions using the optimized process.