Quasi-hexagonal ordered arrays of FePt nanoparticles prepared by a micellar method

Hexagonally ordered arrays of magnetic FePt nanoparticles on Si substrates are prepared by a self assembly of diblock copolymer PS-b-P2VP in toluene, a dip coating process and finally plasma treatment. The as-treated FePt nanoparticles are covered by an oxide layer that can be removed by a 40 s Ar+ sputtering. The effects of the sequence of adding salts on the composition distribution are revealed by x-ray photoelectron spectroscopy measurements. No particle agglomeration is observed after 600 degrees C annealing for the present ordered array of FePt nanoparticles, which exhibits advantages in patterning FePt nanoparticles by a micellar method. Moreover, magnetic properties of the annealed FePt nanoparticles at room temperature are investigated by a vibrating sample magnetometer.

聚苯乙烯-聚（左旋-乳酸）嵌段共聚物薄膜的相分离与结晶

本论文以对称的半结晶型的聚苯乙烯-聚（左旋-乳酸）（PS-b-PLLA）嵌段共聚物薄膜为研究对象，通过在不同厚度的膜中的时间相关的相行为的演变，来研究不同界面对嵌段共聚物薄膜熔融状态的相结构的影响，并以此相结构为模版来研究软硬受限下结晶对相分离的影响。 首先，我们研究了在不同厚度膜中的熔融状态的相结构。通过调控膜的厚度及退火时间，实现片层方向的转变。随着膜厚的增加，由于选择性的聚合物/基板界面及中性的聚合物/空气界面的作用下，达到平衡态后片层方向由平行向垂直转变。当膜厚大于一个周期时，同一膜厚下，随着退火时间的增加，片层方向由平行向垂直转变。片层方向在由平行向垂直的转变时，形成平行与垂直共存的混合结构。 在熔融状态下得到结晶的PLLA在表面对称润湿的平行片层，以这种结构为模版，研究了系留在PS基板上的PLLA单层的结晶，以及结晶对相分离结构的影响。从有序的熔融状态结晶后，形成了上下非晶中间结晶的“三明治”结构，结晶结构为α晶型正交晶系，结晶分子链垂直于界面。当Tc ≤ Tg,PS, 时，由于分子链的活动性较差，而且 PS与PLLA具有相近的表面能，结晶诱导了垂直片层的形成。当Tc > Tg,PS, 由于分子链的活动性较强，没有形成垂直片层。 以中性的聚合物/空气界面作用下形成的垂直片层为模版，研究了软硬受限条件下结晶对垂直片层结构演变的影响。硬受限下，结晶没有破坏相分离结构，在微相分离的垂直片层中受限结晶，结晶后片层周期增加。软受限下，非晶的PS分子链的活动性较强，结晶破坏了原有的相分离结构，生成棒状结晶。由于受限，结晶结构较为特殊属于单斜晶系。 以平行与垂直片层共存的混合结构为模版，研究了结晶对此结构的影响，发现平行与垂直片层分别结晶形成不同的结晶形貌，两种结晶在形成的过程中相互影响。

可生物降解的两亲性嵌段共聚物的自聚集行为研究

可生物降解的两亲性嵌段共聚物PLA-PEG飞所制备的胶束或纳术粒子，作为潜在的药物控制释放体系弓！起人们广泛的兴趣。，方们授有寿比山于PEG链的空间位阴．效应可以避免单核噬菌体的吞噬，、并且可以通过控制可降解部分的降解行为实现药物的持续释放，使在微载体内所包载的药物分子持续释放出来。尽管高聚物的胶束和纳米粒子作为药物的胶体载体已作厂泛研究，但是对其本身物理化学性质与应用之间的联系研究甚少。因此本文对一系列PLLA和PEG两嵌段和三嵌段共聚物的自聚集行为进行了细致研究，得到了以卜结论：1．以花为"模型药物"，通过荧光探针技术对一系列两亲性共聚物在水呀招夜和NaCI溶液种的胶束化行为进行了研究。这些共聚物是由一种新型氨钙催化利，以人分J，的聚乙二醇（PEG）为引发剂，引发丙交酷开环聚合得到，，其中囚定长度阴 PEG段分剐为44，104和113环氧乙烷早兀，PLLA的长没在15-280乳酸中元之间。由于氨钙准活性的特点，这些共聚物的分散度较低，均在1.1-1.3之间。其临界胶束浓度cmc发现随PLLA的含量增加I荆氏。具有同一PEG长度的两嵌段和三嵌段共聚物cmc值的截然差别为它们胶束的构型不同提供了证据。同时也发现了NaCI的加入对丫EG段和争LLA段较短洪聚物的cmc的降低有明掀笋作用，而对具有较长PEG段或较长PLLA段的共聚物的cmc基本上没有什么影响。2．通过荧光探余十技术测定花在这一系列共聚物胶束溶液锄勺配分系数在0.2*10~5至1.9*10~5之间，对于同-PEG段的共聚物，花在其胶柬相中的配分系数随PLLA的含量的增加而增加。另外发现NaCl的加入能够促进花在胶束相中的配分。3．通过透射电子显微镜研究了两嵌段共聚物水溶液胶束的形貌，发现胶束的粒径和分散度均随PLLA段的增加而增加：通过原子力显微镜研究"这些纳米粒子退火前后的形貌变化，发现退火后纳米粒子重新自聚集为类似于神经网络红脚乏的"纳米条带"结构，其中心为类似"神经元"的团簇结构，而周困为支化的车由突"分支结构，这与文献上提到的只有三嵌段共聚物能够形成支化的"纳米条带"结构截然不同，其自聚集机理在进，步研究之中。4．以亲水性的荧光素为荧光探针研究了两嵌段共聚物在甲苯中的胶束化行为，发现其clnc值随PLLA段的含量增加而降低，相对于PEG段，PLLA段在其胶宋化过程中起主要作用。通过1HNMR证明两嵌段共聚物在甲苯中的胶束具伯以PLLA段为"核"、PEG段为"壳"的"核-壳"结构，这种胶柬化行为通过溶解度参数的差异进行了解释。5.通过原子力显微镜发现，当这些胶束滴加在云母表面上经过热处理后，这些胶束重新自聚集成为规则的具有平缓隆起的纳米结构，这与由水中得到的胶柬热处理后的形貌截然不同，并对此进行了进一步解释。由XPS分析认为主要是PEG段覆盖在PLLA段表面。

Biodegradable Interpolyelectrolyte Complexes Based on Methoxy Poly(ethylene glycol)-b-poly(alpha,L-glutamic acid) and Chitosan

We synthesized methoxy poly(ethylene glycol)-b-poly(alpha,L-glutamic acid) (mPEGGA) diblock copolymer by ring-opening polymerization of N-carboxy anhydride of gamma-benzyl-L-glutamate (NCA) using amino-terminated methoxy polyethylene glycol (mPEG) as macroinitiator. Polyelectrolyte complexation between mPEGGA as neutral-block-polyanion and chitosan (CS) as polycation has been scrutinized in aqueous solution as well as in the solid state.

Rigidity effect on phase behavior of symmetric ABA triblock copolymers: A Monte Carlo simulation

The phase behavior of symmetric ABA triblock copolymers containing a semiflexible midblock is studied by lattice Monte Carlo simulation. As the midblock evolves from a fully flexible state to a semiflexible state in terms of increase in its persistence length, different phase behaviors are observed while cooling the system from an infinite high temperature to a temperature below T-ODT (order-disorder transition temperature). Within the midblock flexibility range we studied (l(p)/N-c <= 0.105), a lamellar structure is formed at equilibrium state as the situation for fully flexible chains. The fraction of bridge chain is evaluated for the lamellar structures. We find that the increase in midblock rigidity indeed results in the increase in bridge chain fraction within the range from 44.9% to 51.8%.

Novel pH- and temperature-responsive block copolymers with tunable pH-responsive range

A series of novel pH- and temperature-responsive diblock copolymers composed of poly(N-isopropylacrylamide) (PNIPAM) and poly[(L-glutamic acid)-co-(gamma-benzyl L-glutamate)] [P(GA-co-BLG)] were prepared. The influence of hydrophobic benzyl groups on the phase transition of the copolymers was studied for the first time. With increasing BLG content in P(GA-co-BLG) block, the thermal phase transition of the diblock copolymer became sharper at a designated pH and the critical curve of phase diagram of the diblock copolymer shifted to a higher pH region.

The release behavior of doxorubicin hydrochloride from medicated fibers prepared by emulsion-electrospinning

The release behavior of a water-soluble small molecule drug from the drug-loaded nanofibers prepared by emulsion-electrospinning was investigated. Doxorubicin hydrochloride (Dox), a water-soluble anticancer agent, was used as the model drug. The laser scanning confocal microscopic images indicated that the drug was well incorporated into amphiphilic poly(ethylene glycol)-poly(L-lactic acid) (PEG-PLA) diblock copolymer nanofibers, forming "core-sheath" structured drug-loaded nanofibers.

Study of morphology and phase diagram of the H-shaped (AC)B(CA) ternary block copolymers using self-consistent field theory

By using a combinatorial screening method based on the self-consistent field theory (SCFT) for polymer systems, the micro-phase morphologies of the H-shaped (AC)B(CA) ternary block copolymer system are studied in three-dimensional (3D) space. By systematically varying the volume fractions of the components A, B, and C, six triangle phase diagrams of this H-shaped (AC)B(CA) ternary block copolymer system with equal interaction energies among the three components are constructed from the weaker segregation regime to the strong segregation regime, In this study, thirteen 3D micro-phase morphologies for this H-shaped ternary block copolymer system are identified to be stable and seven 3D microphase morphologies are found to be metastable.

Crystal Growth Transition from Flat-On to Edge-On Induced by Solvent Evaporation in Ultrathin Films of Polystyrene-b-Poly(ethylene oxide)

The transition of lamellar crystal orientation from flat-on to edge-on in ultrathin films of polystyrene-b-poly(ethylene oxide) (PS-b-PEO) via solvent vapor (toluene) treatment Was investigated. When the as-prepared film was treated in saturated solvent vapor, breakout crystals could form quickly, and then they transformed from square single crystals (flat-on lamellae) to dendrites and finally to nanowire crystals (edge-on lamellae). Initially, heterogeneous nucleation tit the polymer/substrate interface dominated the structure evolution, leading to flat-on lamellar crystals orientation. And the transition from faceted habits to dendrites indicated a transition of underlying mechanism from nucleation-controlled to diffusion-limited growth. As the solvent molecules gradually diffused into the polymer/substrate interface, it will subsequently weaken the polymer-substrate interaction.

Crystalline morphology of poly(L-lactic acid) thin films

Crystalline morphologies of spin-coated poly(L-lactic acid) (PLLA) thin films under different conditions are investigated mainly with atomic force microscopy (AFM) technique. When PLLA concentration in chloroform is varied from 0.01 to 1% gradually, disordered structure, rod-shape and larger spheres aggregates are observed in thin films subsequently. Under different annealing temperature, such as at 78, 102, 122 degrees C, respectively, we can find most rod-like crystalline aggregates. Interestingly, we observed that nucleation sites locate at the edge of the holes at the original crystalline stage. Then, these holes developed to form chrysanthemum-like and rods subsequently with annealing time meanwhile the size and the shape of crystalline aggregate are changed. In addition. effect of substrate and solvent on morphology is also discussed. On the other hand, the possible mechanism of crystalline morphology evolution is proposed.

Study of self-assembly of symmetric coil-rod-coil ABA-type triblock copolymers by self-consistent field lattice method

The self-assembly of symmetric coil-rod-coil ABA-type triblock copolymer melts is studied by applying self-consistent field lattice techniques in a three-dimensional space. The self-assembled ordered structures differ significantly with the variation of the volume fraction of the rod component, which include lamellar, wave lamellar, gyroid, perforated lamellar, cylindrical, and spherical-like phases. To understand the physical essence of these phases and the regimes of occurrence, we construct the phase diagram, which matches qualitatively with the existing experimental results. Compared with the coil-rod AB diblock copolymer, our results revealed that the interfacial grafting density of the separating rod and coil segments shows important influence on the self-assembly behaviors of symmetric coil-rod-coil ABA triblock copolymer melts. We found that the order-disorder transition point changes from f(rod)=0.5 for AB diblock copolymers to f(rod)=0.6 for ABA triblock copolymers. Our results also show that the spherical-like and cylindrical phases occupy most of the region in the phase diagram, and the lamellar phase is found stable only at the high volume fraction of the rod.

Surface morphology evolution of poly (styrene-block-4-vinylpyridine) (PS-b-P4VP)(H+) and poly(methyl methacrylate)-dibenzo-18-crown-6-poly(methyl methacrylate) (PMCMA) supramolecular film

Well-ordered nanostructured polymeric supramolecular thin films were fabricated from the supramolecular assembly of poly(styrene-block-4-vinylpyridine) (PS-b-P4VP)(H+) and poly(methyl methacrylate)-dibenzo-18-crown-6-poly(methyl methacrylate) (PMCMA). A depression Of cylindrical nanodomains was formed by the block of P4VP(H+) and PMCMA associates surrounded by PS. The repulsive force aroused from the incompatibility between the block of P4VP(H+) and PMCMA was varied through changing the molecule weight (M-w) of PMCMA, the volume fraction of the block of P4VP(H+), and annealing the film at high temperature. Increasing the repulsive force led to a change of overall morphology from ordered nanoporous to featureless structures. The effects of solvent nature and evaporation rate on the film morphology were also investigated. Further evolution of surface morphologies from nanoporous to featureless to nanoporous structures was observed upon exposure to carbon bisulfide vapors for different treatment periods. The wettability of the film surface was changed from hydrophilicity to hydrophobicity due to the changes of the film surface microscopic composition.

Self-assembly of polypeptide-containing ABC-type triblock copolymers in aqueous solution and its pH dependence

Self-assembling of novel biodegradable ABC-type triblock copolymer poly(ethylene glycol)-poly(L-lactide)-poly(L-glutamic acid) (PEG-PLLA-PLGA) is studied. In aqueous media, it self-assembles into a spherical micelle with the hydrophobic PLLA segment in the core and the two hydrophilic segments PEG and PLGA in the shell. With the lengths of PEG and PLLA blocks fixed, the diameter of the micelles depends on the length of the PLGA block and on the volume ratio of H2O/dimethylformamide (DMF) in the media. When the PLGA block is long enough, morphology of the self-assembly is pH-dependent. It assembles into the spherical micelle in aqueous media at pH 4.5 and into the connected rod at or below pH 3.2. The critical micelle concentration (cmc) of the copolymer changes accordingly with decreasing solution pH. Both aggregation states can convert to each other at the proper pH value. This reversibility is ascribed to the dissociation and neutralization of the COOH groups in the LGA residues. When the PLGA block is short compared to the PEG or PLLA block, it assembles only into the spherical micelle at various pH values.

A stable PEO-tethered PDMS surface having controllable wetting property by a swelling-deswelling process

A PEO-tethered layer on a PDMS (polydimethylsiloxane) cross-linked network has been prepared by a swelling-deswelling process. During swelling, the PDMS block of a PDMS-b-PEO diblock copolymer penetrates into the PDMS substrate and interacts with PDMS chains because of the van der Waals force and hydrophobic interaction between them. Upon deswelling, the PDMS block is trapped in the PDMS matrix while the PEO, as a hydrophilic block, is tethered to the surface. The PEO-tethered layer showed stability when treated in water for 16 h. The surface fraction of PEO and the wetting property of the PEO-tethered PDMS surface can be controlled by the cross linking density of the PDMS matrix. A patterned PEO-tethered layer on a PDMS network was also created by microcontact printing and water condensation figures (CFs) were used to study the patterned surface with different wetting properties.