Використання лазерних діодів в рейтресінговій аберометрії

Аберометри є найбільш досконалими офтальмологічними приладами, оскільки вони дозволяють оцінювати сумарну аберацію оптичної системи ока. Однак, їх основним недоліком є висока вартість. Одним із чинників, який визначає вартість аберометра, є використання складної оптико-механічної системи керування лазерним променем, який використовують для рейтресінгу – сканування зіниці ока і сітківки

Bicontinuous Ceramics with High Surface Area from Block Copolymer Templates

Mesoporous polymers with gyroid nanochannels can be fabricated from the self-assembly of degradable block copolymer, polystyrene-<i>b</i>-poly­(l-lactide) (PS-PLLA), followed by hydrolysis of PLLA block. Well-defined polymer/ceramic nanohybrid materials with inorganic gyroid nanostructures in a PS matrix can be obtained by using the mesoporous PS as a template for sol–gel reaction. Titanium tetraisopropoxide (TTIP) is used as a precursor to give a model system for the fabrication of metal oxide nanostructures from reactive transition metal alkoxides. By controlling the rates of capillary-driven pore filling and sol–gel reaction, the templated synthesis can be well-developed. Also, by taking advantage of calcination, bicontinuous TiO₂ with controlled crystalline phase (i.e., anatase phase) can be fabricated after removal of the PS template and crystallization of TiO₂ by calcination leading to high photocatalytic efficiency. This new approach provides an easy way to fabricate high-surface-area and high-porosity ceramics with self-supporting structure and controlled crystalline phase for practical applications. As a result, a platform technology to fabricate precisely controlled polymer/ceramic nanohybrids and mesoporous ceramic materials can be established

Phase Behavior in Self-Assembly of Inorganic/Poly(4-vinylpyridine)-<i>b</i>-poly(ε-caprolactone) Hybrid

A series of poly(4-vinylpyridine)-b-poly(ε-caprolactone) (P4VP-PCL) diblock copolymers of different composition (namely, various nanostructured phases) were synthesized for hybridization with gold precursors. Interesting phase behavior of gold precursors/P4VP-PCL hybrids was found as evidenced by transmission electron microscopy and small-angle X-ray scattering (SAXS). Consistent with theoretical prediction, phase transformation in the hybrids with PCL-rich P4VP-PCL can be induced by the introduction of the gold precursors. In particular, the phase transformation can be achieved by introducing a very small amount of the gold precursors because of the significant increase in the effective excluded volume of hybridized P4VP microdomain as identified by SAXS experiments through the analysis of the 1D correlation function. This morphological evolution is referred to as the bridging mechanism, suggesting that the PCL block of the P4VP-PCL in the hybrids might play an important role in blocking the interconnection between hybridized P4VP microdomains. In contrast, disordered morphology was observed in the hybrids with P4VP-rich P4VP-PCL because of the strong association between the gold precursors and the P4VP block that might disrupt the ordered phase from microphase separation

Long-Range Ordering of Block Copolymer Cylinders Driven by Combining Thermal Annealing and Substrate Functionalization

This work presents a new method for forming well-defined nanostructured thin films from self-assembled polystyrene-block-poly(l-lactide) (PS-PLLA) on Si wafers with a functionalized SiO2 surface. Large, well-ordered, perpendicular PLLA cylinders in PS-PLLA thin films can be formed using the functionalized substrate. In contrast to random copolymers, a neutral substrate for the PS and PLLA blocks is formed by functionalizing a substrate with hydroxyl-terminated PS (PS-OH) followed by hydroxyl-terminated PLLA (PLLA-OH). The heterogeneous grafting of PS-OH and PLLA-OH can be substantially alleviated using this two-step functionalization. Accordingly, the surface properties can be fine-tuned by controlling the ratio of grafted PS-OH to PLLA-OH to control the orientation of the PLLA cylinders on the functionalized SiO2. Nevertheless, the orientation that is driven by the neutral substrate is surprisingly limited in that the effective length of orienting cylinders is less than twice the interdomain spacing. Thermal annealing at high temperature can yield a neutral air surface, rendering perpendicular PLLA cylinders that stand sub-micrometers from the air surface. Consequently, the neutral substrate can be used to enable truly film-spanning perpendicular cylinders in films to be fabricated using the high-temperature thermal treatment. In addition, the perpendicular cylinders can be laterally ordered by further increasing the annealing temperature. The ability to create these film-spanning perpendicular cylinders in films with a well-ordered texture and sub-micrometer thickness opens up possible applications in nanotechnology

Phase Behavior and Color Tuning of Poly(4-vinylpyridine)-<i>b</i>-poly(ε-caprolactone) Complexed with Chromophores

A series of poly(4-vinylpyridine)-<i>b</i>-poly(ε-caprolactone) (P4VP-PCL) diblock copolymers have been synthesized and used for the formation of nanostructures with tunable colors arising from the association of chromophores with P4VP block in P4VP-PCL. The association of chromophores leads to the bathochromical shifts of charge transfer absorption peaks, resulting in the color appearance into the visible region. To achieve the formation of well-defined nanostructured materials, the phase behavior of the mixtures of chromophore/P4VP-PCL was systematically examined. As evidenced by transmission electron microscopy and small-angle X-ray scattering (SAXS), the phase transformation of self-assembled nanostructures can be easily induced by introducing chromophores due to the association of 2-methylidenepropanedinitrile in the chromophores with the lone-pair electron of nitrogen in P4VP block (that is the increase on the effective volume fraction of P4VP, as identified by SAXS experiments through the analysis of one-dimensional correlation function). As a result, by taking advantage of charge transfer and corresponding morphologies from transformation, well-defined nanostructured films resulting from mixing of chromophore and P4VP-PCL offer the possibility to create stimuli-responsive nanomaterials with tunable color

Controlled Ordering of Block Copolymer Gyroid Thin Films by Solvent Annealing

This work presents an approach to achieve controlled ordering of polystyrene-<i>block</i>-poly­(l-lactide) (PS–PLLA) gyroid thin films on a neutral substrate using solvent annealing. Interesting morphological evolution from gyroid to cylinder can be found while using a partially selective solvent for the PS block to anneal the PS–PLLA thin film. To acquire a thin-film sample with thermodynamically stable gyroid morphology, a nonpreferential solvent should be used for solvent annealing to enable controlled ordering of gyroid thin film with the (211)_G plane parallel to the air surface and also the functionalized substrate. By taking advantage of degradable character of the PLLA block, nanoporous PS with well-defined texture can be fabricated by hydrolysis and used as a template for synthesis of various nanohybrids and nanoporous materials

In-Situ Formation of CdS Nanoarrays by Pore-Filling Nanoporous Templates from Degradable Block Copolymers

In-Situ Formation of CdS Nanoarrays by Pore-Filling Nanoporous Templates from Degradable Block Copolymer

Controlled Self-Assembly of Polystyrene-<i>block</i>-Polydimethylsiloxane for Fabrication of Nanonetwork Silica Monoliths

Herein, this work aims to carry out controlled self-assembly of single-composition block copolymer for the fabrication of various nanonetwork silica monoliths. With the use of lamellae-forming polystyrene-block-polydimethylsiloxane (PS-b-PDMS), nanonetwork-structured films could be fabricated by solvent annealing using a PS-selective solvent (chloroform). By simply tuning the flow rate of nitrogen purge to the PS-selective solvent for the controlled self-assembly of the PS-b-PDMS, gyroid- and diamond-structured monoliths can be formed due to the difference in the effective volume of PS in the PS-b-PDMS during solvent annealing. As a result, well-ordered nanonetwork SiO2 (silica) monoliths can be fabricated by templated sol–gel reaction using hydrofluoric acid etched PS-b-PDMS film as a template followed by the removal of the PS. This bottom-up approach for the fabrication of nanonetwork materials through templated synthesis is appealing to create nanonetwork materials for various applications

Association Strength of Metal Ions with Poly(4-vinylpyridine) in Inorganic/Poly(4-vinylpyridine)-<i>b</i>-poly(ε-caprolactone) Hybrids

A series of inorganic/poly(4-vinylpyridine)-b-poly(ε-caprolactone) (P4VP−PCL) hybrids were prepared to examine the phase behavior of hybridization. Various metal ions including Au3+, Cu2+, Cu+, and Ag+ ions were used for the hybridization. As demonstrated by transmission electron microscopy, the phase transformation of self-assembled nanostructures can be easily induced by adding small amount of metal ions due to the association of metal ions with P4VP block that profoundly creates the extra volume in P4VP microdomain (i.e., gives rise to the significant increase of effective excluded volume) beside the Ag+ ions. The variation in the effective excluded volume (relevant to the degree of domain swelling, as evidenced by small-angle X-ray scattering) is strongly dependent upon the association strength of the metal ions with the P4VP block, as determined by Fourier transform infrared spectroscopy. The association strength for the formation of the hybrids follows the order of Au3+ > Cu2+ and Cu+ > Ag+. Accordingly, the degree of domain swelling in the hybrids increases with the enhancement of association strength following the order of Au3+ > Cu2+ and Cu+ > Ag+. Furthermore, as demonstrated in the hybrids of Au nanoparticles and P4VP−PCL, a dramatic decrease of the association strength can be found in the hybrids after reduction. Consistent with the theoretical prediction, the reduction of metal ions causes the alleviation of the association strength. The association effect is also dependent upon the particle size; the larger the particle size is, the weaker the association will be. Consequently, the accommodation of the metal nanoparticles within the P4VP microdomain is justified by the size of the metal nanoparticles

Syntheses of Stereoregular Amorphous−Crystalline Diblock Copolymers and Their Self-Assembly Studies

The syndiotactic polypropylene-block-atactic polystyrene (sPP-b-aPS), a novel crystalline−amorphous stereoregular diblock copolymer, is prepared in two steps. First, p-methylstyrene-capped syndiotactic polypropylene (pMS-capped sPP), which served as an end-functionalized prepolymer, can be successfully prepared by conducting propylene polymerization in the presence of p-methylstyrene and hydrogen using Me2C(Cp)(Flu)ZrCl2 as the catalyst. Second, the resulting end-functionalized prepolymer is linked to polystyrene (aPS) to provide the stereoregular crystalline−amorphous diblock copolymer, sPP-b-aPS, with a narrow range of molecular weight distribution (MWD). The resulting stereoregular crystalline−amorphous diblock copolymer, sPP-b-aPS, is able to self-organize into ordered nanopatterns in bulk as revealed by bright field transmission electron microscopy analyses