The crystallization of highly isotactic polypropylene confined in self-ordered nanoporous alumina is studied by differential scanning calorimetry. A transformation from a predominantly heterogeneous to predominantly homogeneous nucleation takes place if the pore diameter is smaller than 65 nm. Crystallization is suppressed with decreasing pore size, and the absence of nucleation below 20 nm pores indicates the critical nucleus size. The results reported here might enhance the understanding of nanocomposites containing semicrystalline polymers and reveal design criteria for polymeric nanofibers with tailored mechanical and optical properties.

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The crystallization and local dynamics of poly(3-caprolactone) (PCL) confined to self-ordered nanoporous alumina (AAO) were studied as a function of pore size, pore surface functionality, molecular weight and cooling/heating rate by differential scanning calorimetry (DSC), wide-angle X-ray diffraction and dielectric spectroscopy. In contrast to the bulk, PCL located inside nanoporous alumina crystallizes via several distinct nucleation mechanisms. All mechanisms display pronounced rate dependence. At low undercoolings, the usual heterogeneous nucleation of bulk PCL was suppressed at the expense of two additional mechanisms attributed to heterogeneous nucleation initiated at the pore walls. At higher undercoolings a broad peak was observed in DSC which we attribute to crystallization initiated by homogeneous nucleation. At high cooling rates, the critical nucleus size is smaller than the smallest diameter of pores. Thus, PCL is able to crystallize within the smallest pores, despite the lower degree of crystallinity. Inevitably, homogeneous nucleation is strongly coupled to the local viscosity and hence to the local segmental dynamics. Dielectric spectroscopy revealed that confinement affected both the rate of segmental motion with a lowering of the glass temperature as well as a broader distribution of relaxation times.

The nematic-to-isotropic, crystal-to-nematic, and supercooled liquid-to-glass temperatures are studied in the liquid crystal 4-pentyl-4'-cyanobiphenyl (5CB) confined in self-ordered nanoporous alumina. The nematic-to-isotropic and the crystal-to-nematic transition temperatures are reduced linearly with the inverse pore diameter. The finding that the crystalline phase is completely suppressed in pores having diameters of 35 nm and below yields an estimate of the critical nucleus size. The liquid-to-glass temperature is reduced in confinement as anticipated by the model of rotational diffusion within a cavity. These results provide the pertinent phase diagram for a confined liquid crystal and are of technological relevance for the design of liquid crystal-based devices with tunable optical, thermal, and dielectric properties.

A novel branched polyamine (polyethyleneimine, PEI) functionalized mesoporous silica (MS) adsorbent is developed via a facile "grafting-to" approach. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FT-IR) spectroscopy verified the effective surface functionalization of MS with monolayer and polymer. The transmission electron microscopy (TEM) was employed to reveal the morphology of the fabricated materials. The adsorption behavior of the polyamine functionalized mesoporous silica (MS-PEI) is assessed against anionic dyes. The adsorbent characteristics of MS-PEI are compared with a monolayer platform comprising of 3-aminopropyltriethoxy silane (APTES) functionalized mesoporous silica (MS-APTES). The adsorption behavior of the MS-PEI and MS-APTES toward anionic dyes is further evaluated by studying the effect of adsorbent dosage, pH, contact time, and temperature. Langmuir and Freundlich isotherm models are employed to understand the adsorption mechanism. The obtained kinetic data support a pseudo-second-order adsorption behavior for both monolayer and polymer functionalized MS. The associated thermodynamic parameters (ΔG°, ΔH°, and ΔS°) reveal that the process of adsorption with MS-PEI is more spontaneous and energetically favored as compared to the adsorption with MS-APTES. Taken together, the novel adsorbent system derived from a combination of MS and branched polymer (MS-PEI) shows the higher absorption efficiency and capacity toward the anionic dyes than the monolayer based adsorbent (MS-APTES).

Highly efficient removal of mercury(II) ions (Hg(II)) from water has been reported by employing polymer-brush-functionalized magnetic nanoparticles (MNPs). Surface-initiated conventional radical polymerization (SI-cRP) was used to grow poly(2-aminoethyl methacrylate hydrochloride) (poly-AEMA·HCl) polymer chains on magnetite nanoparticles (Fe3O4), followed by the transformation of pendant amino groups into dithiocarbamate (DTC) groups, which showed high chelating affinity toward Hg(II) ions. This polymer-brush-based DTC-functionalized MNP (MNPs-polyAEMA·DTC) platform showed the complete removal of Hg(II) from aqueous solutions. The Hg(II) ion removal capacity and efficiency of MNPs-polyAEMA·DTC were compared with its monolayer analogue, which was derived from the direct transformation of amino groups of (3-aminopropyl) triethoxysilane (APTES)-functionalized MNPs (MNPs-APTES) to DTC functional groups (MNPs-DTC). The surface chemical modifications and higher chelating functional group density, in the case of MNPs-polyAEMA·DTC, were ascertained by transmission electron microscopy (TEM), thermogravimetric analysis (TGA), physical property measurement system (PPMS), attenuated total reflectance infrared (ATR-IR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). The Hg(II) ion removal capacity and efficiency of monolayer and polymer-brush-based DTC-functionalized MNPs (MNPs-DTC and MNPs-polyAEMA·DTC, respectively) were evaluated and compared by studying the effect of various factors on the percentage removal of Hg(II) such as adsorbent amount, temperature, and contact time. Furthermore, the adsorption behavior of MNPs-DTC and MNPs-polyAEMA·DTC was analyzed by applying Langmuir and Freundlich adsorption isotherm models. In addition, the adsorption thermodynamics, as well as the adsorption kinetics, were also evaluated in detail. The higher surface functional group density of MNPs-polyAEMA·DTC led to superior remediation characteristics toward Hg(II) ions than its monolayer analogue.

The nucleation mechanism of water can be precisely regulated by confinement within nanoporous alumina. We found a transition from heterogeneous nucleation of hexagonal ice (Ih) to homogeneous nucleation of predominantly cubic ice (Ic) with decreasing pore diameter. These results lead to a phase diagram of water under confinement. It contains a (stable) predominant Ic form, a form known to exist only in the upper atmosphere. Possible applications range from cryopreservation to construction materials like cement.

The kinetics of crystallization (heterogeneous vs homogeneous nucleation) and the relation to the local segmental dynamics are studied in a series of poly(ethylene oxide)-b-poly(ε-caprolactone) (PEO-b-PCL) diblock copolymers confined within self-ordered nanoporous alumina (AAO) by X-ray scattering, polarizing optical microscopy, differential scanning calorimetry and dielectric spectroscopy. In the bulk and for the more asymmetric copolymer, the minority phase (PEO) nucleates solely via homogeneous nucleation. When the same diblock copolymers reside inside AAO, nucleation of PEO is completely suppressed. The majority block (PCL) is also affected by confinement and crystallizes at lower temperatures via homogeneous nucleation. These findings can be discussed in terms of the proposed temperature vs curvature "phase diagram". In this diagram the melt and glassy states are separated by the two nucleation regimes, heterogeneous and homogeneous at high and low temperatures, respectively. Homogeneous nucleation is controlled by the faster part of the distribution of PCL segmental relaxation which under confinement speeds-up.