In situ observation of water behavior at the surface and buried interface of a low-k dielectric film

Probing Interfacial Behavior and Antifouling Activity of Adsorbed Copolymers at Solid/Liquid Interfaces

Polymers containing poly(ethylene glycol) (PEG) units can exhibit excellent antifouling properties, which have been proposed/used for coating of biomedical implants, separation membranes, and structures in marine environments, as well as active ingredients in detergent formulations to avoid soil redepositioning in textile laundry. This study aimed to elucidate the molecular behavior of a copolymer poly(MMA-co-MPEGMA) containing antiadhesive PEG side chains and a backbone of poly(methyl methacrylate), at a buried polymer/solution interface. Polyethylene terephthalate (PET) was used as a substrate to model polyester textile surfaces. Sum frequency generation (SFG) vibrational spectroscopy was applied to examine the interfacial behavior of the copolymer at PET/solution interfaces in situ and in real time. Complementarily, copolymer adsorption on PET and subsequent antiadhesion against protein foulants were probed by quartz-crystal microbalance experiments with dissipation monitoring (QCM-D). Both applied techniques show that poly(MMA-co-MPEGMA) adsorbs significantly to the PET/solution interface at bulk polymer solution concentrations as low as 2 ppm, while saturation of the surface was reached at 20 ppm. The hydrophobic MMA segments provide an anchor for the copolymer to bind onto PET in an ordered way, while the pendant PEG segments are more disordered but contain ordered interfacial water. In the presence of considerable amounts of dissolved surfactants, poly(MMA-co-MPEGMA) could still effectively adsorb on the PET surface and remained stable at the surface upon washing with hot and cold water or surfactant solution. In addition, it was found that adsorbed poly(MMA-co-MPEGMA) provided the PET surface with antiadhesive properties and could prevent protein deposition, highlighting the superior surface affinity and antifouling performance of the copolymer. The results obtained in this work demonstrate that amphiphilic copolymers containing PMMA anchors and PEG side chains can be used in detergent formulations to modify polyester surfaces during laundry and reduce deposition of proteins (and likely also other soils) on the textile.

Insights on the Molecular Characteristics of Molecularly Imprinted Polymers as Monitored by Sum Frequency Generation Spectroscopy

Sensing in molecularly imprinted polymers (MIPs) requires specific interactions of the imprinted polymer and the approaching template molecule. These interactions are affected by the morphology of the polymer surface, the affinity of the template molecule to the polymer network, and the steric approach. In this particular study, a template molecule, metronidazole, is studied with respect to the typically used methacrylic acid-based imprinted polymer using a combination of bulk and surface techniques. The resulting infrared (IR) spectra exhibited the presence of the template molecule in the polymer matrix as well as their efficient removal after washing. Dipping of the MIP according to what is expected of facile sensing in an aqueous solution of metronidazole did not show any presence of the template molecule in the bulk of the MIP, as observed by IR spectroscopy. However, using sum frequency generation (SFG) spectroscopy, the CH aromatic stretch of the imidazole ring positioned at ∼3100 cm^-1 was observed at the polymer surface, including its inner pores or cavities, and at the buried polymer-fused silica interface after dipping. SFG studies have also shown the vibrational signatures of the polymer matrix, the presence of the template molecule on the surface, and the detection of residual template molecules after washing. Increasing the washing time to 50 min has proven to be less effective than increasing the washing cycles to three. However, after the third cycle, reorganization of the polymer matrix was evident as also the complete removal of the template molecule. The observed changes from the acquired images using scanning electron microscopy and atomic force microscopy show the structural morphologies of MIPs and a good distribution of the pores across the MIP surface. The study demonstrates the importance of combining both bulk and surface characterization in providing insight into the template molecule-polymer network interactions.

Water as a tuneable solvent: a perspective

Water is the most sustainable solvent, but its polarity limits the solubility of non-polar solutes. Confining water in hydrophobic nanopores could be a way to modulate water solvent properties and enable using water as tuneable solvent (WaTuSo).

Structures and Adhesion Properties at Polyethylene/Silica and Polyethylene/Nylon Interfaces

The molecular structures of buried interfaces of maleic anhydride grafted and ungrafted polyethylene films with silica and nylon surfaces were studied in situ using sum-frequency generation (SFG) vibrational spectroscopy. Grafting maleic anhydride to polyethylene altered the molecular structures at buried interfaces, including changing the orientation of polymer methylene groups and resulting in the presence of C═O groups at silica interfaces. These molecular level changes are correlated with enhanced adhesion properties, with ordered C═O groups and in-plane orientation of the methylene groups associated with higher levels of adhesion. While improved adhesion was observed for grafted polyethylene at the nylon interface, no C═O groups were detected at the interface using SFG, for films thermally treated at 185 °C. In this case, either no C═O groups are present at the interface or they are disordered; the latter explanation is more likely, considering the observed improvement in adhesion.

Water at surfaces with tunable surface chemistries

Aqueous interfaces are ubiquitous in natural environments, spanning atmospheric, geological, oceanographic, and biological systems, as well as in technical applications, such as fuel cells and membrane filtration. Where liquid water terminates at a surface, an interfacial region is formed, which exhibits distinct properties from the bulk aqueous phase. The unique properties of water are governed by the hydrogen-bonded network. The chemical and physical properties of the surface dictate the boundary conditions of the bulk hydrogen-bonded network and thus the interfacial properties of the water and any molecules in that region. Understanding the properties of interfacial water requires systematically characterizing the structure and dynamics of interfacial water as a function of the surface chemistry. In this review, we focus on the use of experimental surface-specific spectroscopic methods to understand the properties of interfacial water as a function of surface chemistry. Investigations of the air-water interface, as well as efforts in tuning the properties of the air-water interface by adding solutes or surfactants, are briefly discussed. Buried aqueous interfaces can be accessed with careful selection of spectroscopic technique and sample configuration, further expanding the range of chemical environments that can be probed, including solid inorganic materials, polymers, and water immiscible liquids. Solid substrates can be finely tuned by functionalization with self-assembled monolayers, polymers, or biomolecules. These variables provide a platform for systematically tuning the chemical nature of the interface and examining the resulting water structure. Finally, time-resolved methods to probe the dynamics of interfacial water are briefly summarized before discussing the current status and future directions in studying the structure and dynamics of interfacial water.

Importance of Substrate Functionality on the Adhesion and Debonding of a Pressure-Sensitive Adhesive under Water

We investigate the effect of an aqueous environment on the adhesion of a model acrylic pressure-sensitive adhesive (PSA) composed of 2-ethylhexyl acrylate-co-acrylic acid. We use probe-tack adhesion measurements accompanied by in situ imaging of the contact region during bonding and debonding. Within the probe-tack tests, we use both hydrophilic (piranha and plasma treatment) and hydrophobic (C₁₈-silanization) surface treatments to investigate the contribution of the probe's surface energy on the underwater adhesion. In examining contact formation in air and underwater, we find that the presence of water when contact is made leads to different modes of PSA relaxation and contact formation. For all probes investigated, the adhesive strength between the PSA and the probe decreases when measured underwater. Additionally, we observe that the presence of water during debonding has a more pronounced effect on the adhesive strength of the PSA when probed by a hydrophilic surface as opposed to a hydrophobic surface. Using fingering wavelength analysis, we estimate the surface energy of the PSA in situ and find that when submerged in water, the PSA has a significantly higher surface energy compared to in air. Therefore, combining the observation of different modes of contact formation, the increase in surface energy, and the importance of the surface energy of the probe, we suggest that the decrease in adhesive strength in water can be explained by the hydration of the PSA and by trapped water defects between the PSA and the probe.

Broadband Dielectric Spectroscopic Characterization of Thermal Stability of Low-k Dielectric Thin Films for Micro- and Nanoelectronic Applications

In this paper, we discuss the use of broadband microwaves (MW) to characterize the thermal stability of organic and hybrid silicon-organic thin films meant for insulation applications in micro- and nanoelectronic devices. We take advantage of MW propagation characteristics to extract and examine the relationships between electrical properties and the chemistry of prototypical low-k materials. The impact of thermal anneal at modest temperatures is examined to shed light on the thermal-induced performance and reliability changes within the dielectric films. These changes are then correlated with the chemical changes in the films, and could provide basis for rational selection of organic dielectrics for integrated devices.

Sum Frequency Generation Vibrational Spectroscopy for Characterization of Buried Polymer Interfaces

Sum frequency generation vibrational spectroscopy (SFG-VS) has become one of the most appealing technologies to characterize molecular structures at interfaces. In this focal point review, we focus on SFG-VS studies at buried polymer interfaces and review many of the recent publications in the field. We also cover the essential theoretical background of SFG-VS and discuss the experimental implementation of SFG-VS.

Metastatic Ovarian Cancer Can Be Efficiently Treated by Genetically Modified Mesenchymal Stromal Cells

Due to late diagnosis, often recurrence, formation of metastases and resistance to commonly used chemotherapeutics human ovarian carcinoma represents a serious disease with high mortality. Adipose tissue-derived mesenchymal stromal cells (AT-MSC) can serve as vehicles for therapeutic genes and we engineered AT-MSC to express either Herpes simplex virus thymidine kinase (HSVtk-MSC), which phosphorylates ganciclovir (GCV) to its toxic metabolites or yeast fused cytosine deaminase::uracil phosphoribosyltransferase (CD::UPRT-MSC), which converts 5-fluorocytosine (5-FC) to highly toxic 5-fluorouracil (5-FU). Here, we reported different responses of cytotoxicity mediated by CD::UPRT-MSC/5-FC treatment on human ovarian carcinoma cell lines-SKOV-3 and A2780 used in adherent or three-dimensional (3D) cell culture and we proved high potential of 3D model to predict results in our in vivo experiments. Both tumor cell lines showed similarly high chemosensitivity to the used treatment in adherent culture, but 3D model revealed severe discrepancy-only 36% of SKOV-3 cells but even 90% of A2780 cells were eliminated. This result served as a prognostic marker-we were able to achieve significantly decreased tumor volumes of subcutaneous xenografts of A2780 cells in nude mice and we prolonged tumor-free survival in 33% of animals bearing highly metastatic ovarian carcinoma after CD::UPRT-MSC/5-FC treatment.

Probing the molecular structures of plasma-damaged and surface-repaired low-k dielectrics

A comprehensive characterization on the plasma-damaged and silylation-repaired low-k dielectrics was demonstrated here at the molecular level.

The molecular interfacial structure and plasticizer migration behavior of “green” plasticized poly(vinyl chloride)

Both oxygen and argon plasma treatment made TBAC–PVC surfaces hydrophilic, but that of argon enhanced the migration of TBAC to water.