8 research outputs found
A Comparison of Tackified, Miniemulsion CoreâShell Acrylic Latex Films with Corresponding Particle-Blend Films: StructureâProperty Relationships
Deformation and adhesion of a periodic softâsoft nanocomposite designed with structured polymer colloid particles
Lateral surface nonuniformities in drying latex films
The length scales of film thickness nonuniformities, commonly observed in polymer colloid (i.e., latex) films, are predicted. This prediction is achieved by investigating the stability behavior of drying latex films. A linear stability analysis is performed on a base solution representing a uniformly drying latex film containing a surfactant. The analysis identifies film thickness nonuniformities over two length scales: long (millimeter) range (from lubrication theory) and short (micrometer) range (from nonlubrication theory). Evaporation and surfactant desorption into the bulk film are identified as the primary destabilizing mechanisms during drying. Experimental evidence through direct visualization and atomic force microscopy confirm the existence of nonuniformities over both length scales, which are shown to be functions of parameters such as initial particle volume fraction, surfactant amount, and desorption strength, while being independent of drying rate. © 2008 American Institute of Chemical Engineers AIChE J, 200
Large-Area Patterning of the Tackiness of a Nanocomposite Adhesive by Sintering of Nanoparticles under IR Radiation
We present a simple technique to
switch off the tack adhesion in
selected areas of a colloidal nanocomposite adhesive. It is made from
a blend of soft colloidal polymer particles and hard copolymer nanoparticles.
In regions that are exposed to IR radiation, the nanoparticles sinter
together to form a percolating skeleton, which hardens and stiffens
the adhesive. The tack adhesion is lost locally. Masks can be made
from silicone-coated disks, such as coins. Under the masks, adhesive
island regions are defined with the surrounding regions being a nontacky
coating. When optimizing the nanocompositeâs adhesive properties,
the addition of the hard nanoparticles raises the elastic modulus
of the adhesive significantly, but adhesion is not lost because the
yield point remains relatively low. During probeâtack testing,
the soft polymer phases yield and enable fibrillation. After heating
under IR radiation, the storage modulus increases by a factor of 5,
and the yield point increases nearly by a factor of 6, such that yielding
and fibrillation do not occur in the probeâtack testing. Hence,
the adhesion is lost. Loading and unloading experiments indicate that
a rigid skeleton is created when the nanoparticles sinter together,
and it fractures under moderate strains. This patterning method is
relatively simple and fast to execute. It is widely applicable to
other blends of thermoplastic hard nanoparticles and larger soft particles
Deformation and adhesion of a periodic soft-soft nanocomposite designed with structured polymer colloid particles
Switching Off the Tackiness of a Nanocomposite Adhesive in 30 s via Infrared Sintering
Soft adhesives require an optimum balance of viscous
and elastic
properties. Adhesion is poor when the material is either too solidlike
or too liquidlike. The ability to switch tack adhesion off at a desired
time has many applications, such as in recycling, disassembly of electronics,
and painless removal of wound dressings. Here, we describe a new strategy
to switch off the tack adhesion in a model nanocomposite adhesive
in which temperature is the trigger. The nanocomposite comprises hard
methacrylic nanoparticles blended with a colloidal dispersion of soft
copolymer particles. At relatively low volume fractions, the nanoparticles
(50 nm diameter) accumulate near the film surface, where they pack
around the larger soft particles (270 nm). The viscoelasticity of
the nanocomposite is adjusted via the nanoparticle concentration.
When the nanocomposite is heated above the glass transition temperature
of the nanoparticles (<i>T</i><sub>g</sub> = 130 °C),
they sinter together to create a rigid network that raises the elastic
modulus at room temperature. The tackiness is switched off. Intense
infrared radiation is used to heat the nanocomposites, leading to
a fast temperature rise. Tack adhesion is switched off within 30 s
in optimized compositions. These one-way switchable adhesives have
the potential to be patterned through localized heating