top of page

New dispersing agent for PR57.1

Updated: Nov 23, 2023

When a drop of liquid is placed on a surface it can either:

  • Spread over the surface – it therefore ‘wets’

  • Form a stable drop – it is unable to ‘wet’

Reduction in surface tension of water by addition of a surfactant can make a non-wetting solution into a wetting solution on particular substrates. The ability to wet or not depends upon the surface tension of the solution and the critical surface tension (CST) or surface energy of the solid. The CST is the surface tension of a liquid which will form a contact angle of close to zero measured across the film on that solid, i.e. the liquid spreads over the solid. Glass, with a CST of more than 70 dynes/cm can be wet easier than polypropylene, with a CST of 28. In all cases to wet a substrate quickly and effectively, a surfactant will be required to help reduce the surface tension and overcome the surface energy of the substrate.


The surface energy of different substrates vary. High energy substrates are easier to wet than low energy substrates.

The diagram below shows the relationship between the surface tension of a droplet onto a substrate surface and the contact angle. The shape of a liquid-vapour interface is determined by the Young–Dupre equation, with the contact angle playing the role of a boundary condition via the Young equation.


The simplified equation is: cos Θc = ϒSL – ϒSG / ϒLG ϒSL = Solid–liquid interfacial energy ϒSG = Solid–vapour interfacial energy ϒLG = Surface tension


The conclusions that can be drawn are:

  • A substrate with high surface tension is easily wetted

  • A liquid with a low surface tension wets a substrate easily

In all cases to wet a substrate quickly and effectively, a surfactant will be required to help reduce the surface tension of the droplet or liquid low enough to overcome the surface energy of the substrate.


Surface Energy of Substrates

Substrate

Surface Energy - mN/m

Copper

~ 1000

Aluminium

~ 500

Glass

290

Stainless steel

53

Lino

~45

Polycarbonate

44

Nylon 6

43.9

Nylon 66

42.2

PET G

39

Rigid PVC

37.9

PE 1000

31.6

Acetal

31

Polypropylene

30.5

PTFE

19.4

Static contact angle measurement


One of the most popular ways of measuring contact angles is using the ‘Sessile Drop Technique’. The contact angle of a sessile drop resting on a solid surface is measured using a goniometer. The goniometer is connected to a microscope and video camera.


The drop of the prepared test liquid is released through a fine needle and allowed to drop under gravity onto the substrate whilst filming the action. From the captured image as seen in the first image above the contact angle can be measured either manually or by utilizing the software.


Sessile Drop A Typical Goniometer


Experimental work on various substrates


Below will highlight of the programme of work that we have carried out on various substrates and substances.

Several test liquids were prepared as a 0.5% solution in deionised water and some test substrates consisting of different plastics and metals were utilised.


An FTȦ 200 goniometer equipped with a digital microscope and video capture was used to analyse the sessile drop images.


A detailed list of substrates tested and their recommendations:

Substrate

1st Choice

Biobased

Acetal

Lanwet JH1

Bioloop 56L or T48

Acrylic Sheet

Lanwet JH1

Bioloop 56L or T48

Aluminium

Lanwet JH1

Bioloop 56L

Copper

Lanwet JH1

Galvanised Steel

Lanwet JH1

Glass

Lanwet JH1

Bioloop 84L or T45

Karndean

Lanwet JH1

Lino

Lanwet JH1

Nylon 6

Lanwet JH1

Bioloop 68L or T25

Nylon 66

Lanwet JH1

Bioloop 56L, T25 or T48

PE 1000

Lanwet JH1

PET G

Lanwet JH1

Bioloop 56L

Polycarbonate

Bioloop 56L

Bioloop 56L or 68L

Polypropylene

Lanwet JH1

Bioloop 56L

PTFE

Lanwet JH1

Rigid PVC

Lanwet JH1

Stainless steel

Lanwet JH1

Vinyl Flooring

Lanwet JH1

Bioloop T65

The following photo stills show the test liquid sessile drop after 5 seconds of wetting on a variety of substrates:


Acetal

 

Acrylic Sheet

 

Aluminium

 

Copper

 

Glass

 

Galvanised Steel

 

Karndean Flooring

 

Lino

 

Nylon 6

 

Nylon 66

 

Polyethylene (PE1000)

 

PET-G

 

Polycarbonate

 

Polypropylene

 

PTFE

 

Rigid PVC

 

Stainless Steel

 

Vinyl Flooring

 

508 views0 comments

Comments


bottom of page