One way to produce high order in a block copolymer thin film is by solution casting a thin film and slowly evaporating the solvent in a sealed vessel. Such a solvent-annealing process is a versatile method to produce a highly ordered thin film of a block copolymer. However, the ordered structure of the film degrades over time when stored under ambient conditions. Remarkably, this aging process occurs in mesoscale thin films of polystyrene-polyisoprene triblock copolymer where the monolayer of vitrified 15 nm diameter polystyrene cylinders sink in a 20 nm thick film at 22 °C. The transformation is studied by atomic force microscopy (AFM). We describe the phenomena, characterize the aging process, and propose a semiquantitative model to explain the observations. The residual solvent effects are important but not the primary driving force for the aging process. The study may lead to effective avenue to improve order and make the morphology robust and possibly the solvent-annealing process more effective.

Silver nanocubes were synthesized for the first time in large quantities on gold seed in the presence of a polyelectrolyte using microwave heating for 60–120 s. Our experiment indicates that the polyelectrolyte directs the growth of the particle in a specified crystallographic direction resulting in the faceted particle, i.e. a nanocube. The nanocubes are stable for at least 2 months in ambient conditions.

Structure of complex fluid at mesoscales is influenced by interfacial effects. We describe the dynamic response in such films to sudden change in interfacial tension. In a self-assembled block copolymer film, the monolayer of 15 nm diam cylindrical discrete phases close to the surface commence to sink at an average rate of 0.16 nm/day in response to the interfacial tension change. Surprisingly, this spontaneous planarization occurs, even though the cylinders are covalently stitched to the matrix. A simple model explains the observed behavior. The observation may lead to approaches to tailor the structure of mesoscale thin films of complex fluids for long-range order that are desirable for nanoscale device fabrication.

Block copolymers have long been recognized as scaffolds to pattern nanoparticles to construct hybrid structures for various electronic [1], optical [2,3] and optoelectronic [4] applications. Earlier studies focused on synthesizing nanoparticles selectively on the nanoscopic elements of the block copolymer [5,6] to obtain ordered structures and fabricate nanodevices, such as nanowires [7]. In other studies, the hierarchical self-assembly of nanoparticles in a nanoparticle-block copolymer mixture was demonstrated where the particles were selectively drawn towards one of the components of the ordered block copolymer morphology [8][9][10]. Based on the possibility of coupling the thermodynamic ordering of the block copolymer and the selective interaction of nanoparticles with the components of the block copolymer, spontaneous ordering of nanoparticles is theorized [11][12][13] and experimentally demonstrated [14,15]. In this paper we describe a method to selectively deposit pre-synthesized nanoparticles on a (preformed) ordered block copolymer surface using a simple approach where one of the nanoscopic polymer domains is selectively functionalized using reactive plasma.PS-PI-PS tri-block copolymer, supplied by Dexco, was deposited on a Si (silicon) substrate as a thin film by spincasting a 1% solution in toluene. Spinning speed was 3,000 rpm and spinning time was 30 s. Initial thickness of the film is 26-28 nm as confirmed by ellipsometry. Molecular weights (MW) of the two PS and central PI blocks are 18,000 Daltons each and 64,000 Daltons, respectively. The isoprene block has 92% 1,4 addition. The molecular weight ratio of PS to PI results in cylindrical morphology [16,17]. The film was processed by the "solvent annealing" procedure [17] and then was baked for 20 min in vacuum at 50 °C. Next, the film was exposed to corona discharge performed in 85% relative humidity air under ambient pressure and temperature for 3 min (moderate etching) or 4 min (deep etching), followed by a thorough rinse with DI (deionized) water. After the film was dried with air flow, it was exposed to 45 W ammonia plasma at a pressure of 580 mTorr for 10 s. Immediately after plasma treatment, the film was immersed into 10 nm Au nanoparticle solution (purchased from BBinternational) for 8-24 h. The Au nanoparticle surface is negatively charged by ClO 4 − groups (as-received). Concentration of the Au nanoparticles is 5.7 × 10 12 particles ml −1 . Prior to use, the pH of the Au nanoparticle solution was adjusted by addition of diluted HCl solution (pH = 1.5) to a value of ~5. No salt was added. Finally, the film was vigorously washed with DI water and dried in air flow.In Figure 1, tapping mode atomic force microscope (AFM) images of the film prior to corona treatment (Figure 1(a)), after corona treatment under moderate (Figure 1(b)) and deep etching (Figure 1(c)) are compared. With moderate etching (Figure 1(b)), while the lateral morphology is intact, the height difference between the crest and trough, Δh, is 6 nm, compared AbstractWe have de...

No abstract