Pressure-sensitive Applications Research Articles

Functionalized carbon nanotube reinforced polymer nanocomposite microcapsules with enhanced stiffness

Microcapsules with tunable mechanical properties are highly desirable in pressure sensitive applications. We report here a facile approach to prepare polyurea/multiwall carbon nanotube (MWCNTs) nanocomposite microcapsules (MICs) with enhanced stiffness. A model compound dimethyl phthalate (DMP) was used as core material. MWCNTs were modified with reactive functional groups namely carboxyl (COOH), amines (NH2), and isocyanates (NCO) to ensure a stronger interface between polymer wall and MWCNTs. Functionalization of MWCNTs was corroborated by Fourier transformed infrared spectroscopy (FTIR). Scanning electron microscopy (SEM) was employed to study the surface morphology of MICs. The presence of MWCNTs in the microcapsule wall was confirmed by transmission electron microscopy (TEM). MICs with functionalized MWCNTs show almost 100% increase in stiffness with respect to pristine capsules. All MICs show 92–97 ± 1% encapsulation efficiency. The approach used in this paper can be broadly utilized to tune the mechanical properties of the microcapsules.

Local wettability tuning with laser ablation redeposits on PDMS

In this paper, we present a method to locally control the wettability behavior of PDMS surfaces by excimer laser ablation. In the ablation process, a micrometer scale roughness is formed in the irradiated regions while a nanometer scale roughness is formed by the redeposits surrounding the irradiated regions. The increase in surface roughness results in a change of the wettability behavior of the PDMS surface. By using a hexagonal pattern and tuning the patterning pitch, two different wetting behaviors were realized. A pitch smaller than 300μm resulted in a superhydrophobic surface with an advancing contact angle of θadv=165° and a receding contact angle of θrec=160°. A pitch between 300 and 500μm resulted in a sticky superhydrophobic surface with θadv=120–150° and θrec=80°. The contact angle hysteresis for the latter was larger than for untreated PDMS resulting in very sticky surfaces with high sliding angles. This gives the method great versatility since the two wetting behaviors are very different. By combining both behaviors, local surface features like pinning sites, non-wetting sites, barriers and guides can all be fabricated by a single method. As an application demonstrator of the method, we show that drops can be caught and released depending on size and tilting angle by creating slippery surfaces with sticky barriers. Additionally, the method is ideal for rapid prototyping as it consist of only a single step. It is a direct write method requiring no lithographic mask. Also the process works in ambient atmosphere, so it can be used for temperature or pressure sensitive applications.

Some Recent Approaches To the Development of Acrylic Uv Curable Pressure-Sensitive Adhesives

The goal of this program was to utilize ultraviolet radiation (UV) to cure a series of pressure-sensitive adhesives (PSAs) which would provide properties suitable for "light duty" to "permanent" pressure-sensitive applications. A variety of chemical types were represented among the 36 commercial resins which were screened as tackifiers. Utilizing some of the most promising tackifiers, systematic experimental designs were utilized to evaluate formula composition variables and radiation dosage. Trends in performance vs. type and amount of constituents were developed for oligomers, diluent monomers, cross-linking monomers and other additives—along with variations in light intensity and exposure time. Other formulating approaches were also taken, including "one-step" approaches. A number of diverse compositions are presented as a basis for a discussion of formulation parameters.