Recent literature has shown that the thickness of dip-coated films has a V-shaped dependence on dip-coating rate when very slow rates are included. For supramolecular block copolymer films, small molecule (SM) uptake and film morphology are also rate-dependent, as shown previously for a poly(styrene-b-4-vinylpyridine) (PS−P4VP) block copolymer in THF solutions containing naphthol (NOH) and naphthoic acid (NCOOH). Here, these investigations are extended to p-dioxane, toluene, and CHCl 3 solutions. The V-shaped thickness dependence is validated for each solvent, but with the V minimum displaced to lower dip-coating rates and thicknesses for the solvents with lower vapor pressures (p-dioxane, toluene), thereby decreasing the dip-coating rate range of the "capillarity regime" (slow side of the V) and consequently extending that of the "draining regime" (fast side of the V). The SM/VP uptake ratio varies with the nature of the solvent, particularly in the capillarity regime, where it is higher for solvents that are weak SM-VP hydrogen-bond competitors (toluene, CHCl 3 ). The draining regime generally shows greater SM uptake than the capillarity regime, in some cases reaching the solution ratio, with higher uptake observed for the SM with greater hydrogen-bond strength (NCOOH > NOH). The variation in film morphology with solvent and dip-coating rate (spherical for toluene; spherical and cylindrical for p-dioxane; spherical, cylindrical, and lamellar for THF; and lamellar only for CHCl 3 ; for a block copolymer whose equilibrium morphology in the bulk is near the cylindrical/lamellar phase boundary) depends on the initial solution state (whether micellar or not and hardness of micelles) and the SM uptake ratio. These factors, along with solvent evaporation rate and film thickness, influence the kinetics of morphology development in the drying films, the point at which the kinetics are frozen in, the effective block ratio, and the orientation of the morphological structures.

We demonstrate a unique combination of simultaneous top-down and bottom-up control of the morphology of block copolymer films by application of in situ optical irradiation during dip-coating. A light-addressable and blockselective small molecule, 4-butyl-4'-hydroxyazobenzene (BHAB), is introduced into a diblock copolymer of polystyrene and poly(4-vinylpyridine) (PS-P4VP) of 28.4 wt% P4VP via supramolecular chemistry, notably by hydrogen bonding to P4VP. We show that the spherical morphology of thin films dip-coated from a THF solution at slow withdrawal rates in the dark convert to cylindrical morphology when dip-coated under illumination. This is attributed to volume expansion of the P4VP/BHAB phase due to trans-cis photoisomerization combined with a light-induced increase in BHAB uptake in the film. The demonstrated photocontrol highlights the potential of dip-coating as a scalable film preparation method that can be easily coupled with external stimuli to direct nanostructured self-assembly in the films as solvent evaporates.Controlling the properties of soft materials at the nanoscale is paramount for high-technology applications in diverse domains. Many of these applications require nanostructured materials to be in the form of thin films of good surface quality, 1 for example when used as nanolithographic templates for the electronics industry. 2 Block copolymers (BCPs) are well suited for this purpose, given their propensity to self-assemble into well-defined morphologies, with typical periodicities in the 10-100 nm range, due to block immiscibility. 3 In thin films, this leads to various surface patterns that are controllable at will by a number of parameters, both material (such as molecular weight, block volume fractions, interfacial interaction parameters, and addition of block selective components) and experimental (such as film preparation method, choice of solvent, and thermal/solvent annealing). 1

Dip-coating allows nanostructured block copolymer (BCP) thin film fabrication in a fast and facile one-step process. It can also be coupled with external controls, such as illumination. Herein, we expose several design principles that enable photocontrol of the nanostructured surface pattern and thickness of supramolecular BCP thin films. This is done using a polystyrene-poly(4-vinylpyridine) (PS-P4VP) BCP and two hydroxy-functionalized smallmolecule (SM) azo derivatives that have different photochemical characteristics and that hydrogen bond to the P4VP block. We show how the film preparation concept provides tunability through the chemical structure of the photoactive SM, the relative amount of SM in the dip-coating solution, and the choice of solvent. It was found that the film thickness and SM uptake in the films are increased by illumination when using THF, but are unchanged when using toluene as solvent, which is attributed to an optical heating effect observable with volatile solvents. The photocontrol of surface patterns is a result of photoinduced changes in the effective volume fraction of the P4VP+SM phase, which is increased by greater volume of cis isomers, by higher SM uptake (using THF), and by more trans-cis-trans cycling for systems with shorter cis lifetime. The extent of photoinduced change can also be increased by higher molecular mobility due to more flexible SMs, lower BCP molecular weight, and non-micellar or softer micellar solutions.