PVDF thin films prepared under standard processing conditions have a cloudy appearance and are notoriously rough, which prevent microelectronic and photonic applications. On the other hand, high optical quality, smooth films can be prepared either at low relative humidity or at high substrate temperature. Here we systematically investigate the morphology of PVDF thin films by varying the processing conditions. Films are characterized by SEM and AFM and by measurements of clarity, haze and absorption. We show that the cloudy appearance is due to vapor-induced phase separation (VIPS) as is well-documented for the formation of PVDF membranes. Formation of opaque thin films is a general problem of any ternary polymer/solvent/non-solvent system where a high boiling point solvent is used that is fully miscible with a non-solvent, here water from the ambient.

/pdf/controlling-the-microstructure-of-poly-vinylidene-fluoride-3nke3haajb.pdf

Controlling the microstructure of poly(vinylidene-fluoride) (PVDF) thin films for microelectronics

Photocatalytic, superhydrophilic, self-cleaning TiO 2 coating on cheap, light-weight, flexible polycarbonate substrates

No surface is perfectly flat at every length scale. However, all natural and man-made surfaces show some degree of roughness. Therefore, it is imperative to know how surface disorder may affect physical process at, or in the immediate vicinity, of the surface. In this review, we focus on the long-standing problem of electromagnetic wave scattering from randomly rough surfaces. This topic has implications and practical applications in fields of science and engineering ranging from observational astronomy to the electronic and medical industry. How randomly rough surfaces can be described statistically is outlined, and we introduce the theoretical and computational methods most frequently used in the study of light scattering from randomly rough metal or dielectric surfaces. A large part of the review is devoted to the description and the discussion of the physical origin behind various multiple scattering phenomena that can exist when light interacts with a random surface. Some of the addressed phenomena are; the enhanced backscattering and satellite peak phenomena; forward scattering (specular peak) enhancement; coherent effects in the angular intensity correlation functions and the second harmonic generated light (nonlinear effect).

Optics of surface disordered systems. A random walk through rough surface scattering phenomena

A facile method for simulating randomly rough membrane surface associated with interface behaviors

UV-absorbing nanoparticles (NPs) and microparticles (MPs) were prepared by emulsion and dispersion copolymerization of the vinylic monomer 2-(2′-hydroxy-5′-methacryloxyethylphenyl)-2H-benzotriazole (Norbloc (NB)) with the crosslinking monomer divinylbenzene. The effect of the initiator concentration on the size and size distribution of the polyNB (PNB) particles was elucidated. Thin coatings of the formed PNB NPs or MPs of 19 ± 2 and 200 ± 25 nm dry diameter, respectively, onto polypropylene (PP) films were then prepared and characterized. Increasing the concentration or thickness of the PNB NP or MP thin coatings on the PP films decreased their UV transmittance, up to complete UV blocking with just 2 μm of a 4% NP coating. Migration of the UV-absorbing agents from the coated PP films was not observed during three years of storage at room temperature, offering a unique solution to current problems of migration of UV-absorbing additives. The thin coatings obtained by the PNB NPs were superior to those of t...

Design of UV-Absorbing Polypropylene Films with Polymeric Benzotriaziole Based Nano- and Microparticle Coatings.

he haze of a film is defined as the fraction of (nor-mal incident) transmitted light that deviates fromthe directly transmitted beam by more than 2.5 (1).The contrast of an object seen through a film de-creases with increasing haze. The resolution of detail,a second criterion of transparency, is usually referredto as clarity. From a light scattering point of view,haze corresponds to larger scattering angles than lossof clarity. Note that a reduction in haze not necessarilyleads to improved clarity. Haze due to surface rough-ness is in many cases inversely related to gloss, whichis another important optical property.Both bulk inhomogeneities and surface roughnessmay contribute to haze. The latter effect usually domi-nates for polyethylene (PE) films. The typical scale ofthe roughness relative to the wavelength of light ( )determines the scattering characteristics. The heightvariation of the surface is usually reported to follow aGaussian distribution (2), and optical surfaces areoften characterized by the root-mean-square deviation( ) from the mean surface height. Roughness values, , in the range 20–600 nm are typically reported forPE films, i.e. . The haze increases monotonouslywith increasing roughness. Various techniques havebeen used for characterizing the surface profiles.Atomic force microscopy (AFM), has been applied in anumber of recent studies (3–6).Many types of PE are available for film blowingprocesses. The three main types, low-density (LDPE),linear low-density (LLDPE) and high-density (HDPE),all have their advantanges and drawbacks, also whenit comes to optical properties. Early experimental liter-ature (up to 1981) on the haze of PE blown films wasreviewed by Willmouth (1). The main findings can besummarized as follows. Two main sources of surfaceroughness have been identified: 1) flow-induced irreg-ularities originating from the die, and 2) protrudingcrystalline structures (lamellae, stacks of lamellae orspherulites). The former is a well-known rheologicaleffect, and the resulting extrusion-induced haze isoften observed to increase with increasing melt elas-ticity, e.g. due to more long-chain branching (LCB) or broader molecular weight distribution (MWD). The melt elasticity of LDPE (containing LCB) can be

Haze of polyethylene films—effects of material parameters and clarifying agents

Approximate analytic expressions for haze (and gloss) of Gaussian randomly rough surfaces for various types of correlation functions are derived within phase-perturbation theory. The approximations depend on the angle of incidence, polarization of the incident light, the surface roughness, $\ensuremath{\sigma}$, and the average of the power spectrum taken over a small angular interval about the specular direction. In particular it is demonstrated that haze (gloss) increase (decrease) with $\ensuremath{\sigma}/\ensuremath{\lambda}$ as $\text{exp}[\ensuremath{-}A{(\ensuremath{\sigma}/\ensuremath{\lambda})}^{2}]$ and decreases (increase) with $a/\ensuremath{\lambda}$, where $a$ is the correlation length of the surface roughness, in a way that depends on the specific form of the correlation function being considered. These approximations are compared to what can be obtained from a rigorous Monte Carlo simulation approach, and a good agreement is found over large regions of parameter space. Some experimental results for the angular distribution of the transmitted light through polymer films and their haze are presented and compared to the analytic approximations derived in this paper. A satisfactory agreement is found. In the literature haze of blown polyethylene films has been related to surface roughness. Few authors have quantified the roughness and others have pointed to the difficulty in finding the correct roughness measure.

http://web.phys.ntnu.no/~ingves/Downloads/MyPapers/PhysRevA_79_063813_2009.pdf

Haze of surface random systems: An approximate analytic approach

An injection moulded or compression moulded article comprising a multimodal high density ethylene hexene copolymer (HDPE) containing at least a lower molecular weight (LMW) polyethylene homopolymer component and a higher molecular weight (HMW) ethylene hexene copolymer component; wherein said HDPE has a MFR2 of 0.1 to 20 g/10min when determined according to ISO 1133 at 190°C at load of 2.16 kg; a density of 945 to 975 kg/m3; a tensile modulus of at least 850 MPa; and an ESCR-B of at least 300h.

Moulded article comprising high density polyethylene copolymer

Gloss is a quantity used in the optical industry to quantify and categorize materials according to how well they scatter light specularly. With the aid of phase perturbation theory, we derive an approximate expression for this quantity for a one-dimensional randomly rough surface. It is demonstrated that gloss depends in an exponential way on two dimensionless quantities that are associated with the surface randomness: the root-mean-square roughness times the perpendicular momentum transfer for the specular direction, and a correlation function dependent factor times a lateral momentum variable associated with the collection angle. Rigorous Monte Carlo simulations are used to access the quality of this approximation, and good agreement is observed over large regions of parameter space.

Estimation of gloss from rough surface parameters

A polyethylene composition comprising at least a first composition and a second composition in amounts of at least 70 wt% of the first composition which comprises at least: (A) up to 60 wt% lower molecular weight (LMW) polyethylene homo or copolymer obtained by Ziegler-Natta catalysis having a density of at least 940 kg/m ; and (B) up to 60 wt% higher molecular weight (HMW) polyethylene homo orcopolymer obtained by Ziegler-Natta catalysis and having lower density than component (A); and up to 30 wt% of the second composition which comprises: (C) a polyethylene homo or copolymer obtained bysingle site catalysis (SSC) and having a density of up to 980 kg/m ; wherein said polyethylene composition has a charpy impact strength at -20 DEG C, according to ISO 179-3 on compression moulded plates of at least 2.5 kJ/m and density at least 925 kg/m .

Katrin Nord-Varhaug

Papers

Haze of polyethylene films—effects of material parameters and clarifying agents

Haze of surface random systems: An approximate analytic approach

Moulded article comprising high density polyethylene copolymer

Estimation of gloss from rough surface parameters

Composition, molded article, membrane and its preparation method and uses