Special application of wetting knowledge...Special application of wetting knowledge Wicking into fibrous materials CONTACT ANGLE ESTIMATION TNT Eva Kuželová Košťáková KCH, FP,

Special application ofwetting knowledge

Wicking into fibrous materialsCONTACT ANGLE ESTIMATION

TNT

Eva Kuželová Košťáková

KCH, FP, TUL

THEORY OF NONWOVENS

-Determining (estimating) the contact angle for porous (fibrous) materials

-Determining (estimating) the contact angle of fibrous swelling materials

- Wicking into structured textiles

THEORY OF NONWOVENS

How to determine the contact angle of

nonwovens (or porous materials in general) for

contact angles of less than 90 °?

Washburn method Washburn theory suggests that if a porous

solid (eg, a nonwoven fabric) comes into contact with a liquid

so that the solid is not immersed in the liquid but rather

touches only the surface of the liquid, then the rise of liquid

into the pores of the solids will result controlled by the

following equation:

Determining (estimating) the contact angle for

porous (fibrous) materials

THEORY OF NONWOVENS

.8

2

h

Pr

dt

dh e

Lucas – Washburn equation

The fiber wetting theory was built

in the 1920s independently by

Lucas and Washburn.

Their approach is based on a

strong simplification of the

multifunctional structure of the fiber

mass into a single capillary.

Inside the capillary fluid is

transported due to surface tension.

The experimental results show that

this highly simplified model gives

qualitatively comparable results

with the fabric transport behavior.

.

8

4

21

h

rpp

dt

dV

pr

r r1 2

2 2

cos cos.

p gh2 cos .

.8

cos

4

cos 2

gr

h

r

dt

dh

bh

a

dt

dh



THEORY OF NONWOVENS

.8

2

h

Pr

dt

dh e

.8

cos

4

cos 2

gr

h

r

dt

dh b

h

a

dt

dh

Wicking(0°,90°

bhab

a

b

ht ln

2

The limit t is found from equation. Then ln(a-bh) and thus a-bh=0. Finally the limit, i.e. the maximal h value is …

Relation can be solved in different ways under the assumption that the second term on the right side can be neglected. (i) gravitation is neglected, g=0; or (ii) a height in a capillary is small, so a notation (h→0) can be accepted

2

1

2

cosKtt

rh

OR

Lucas – Washburn equationDetermining (estimating) the contact angle for


THEORY OF NONWOVENS

https://www.lpdlabservices.co.uk/application_note_list/powder_wetting.php

2

1

2

cosKtt

rh

What does c mean? So the material

constant?

c represents: pore structure, pore size and pore number

in a solid porous material, for example, in a nonwoven

fabric

How to determine the value of c?

Correctly, when plotting a square of mass m2 against time t, it shows a linear region whose slope for known liquid properties

(, ρ and η) contains only two unknown c and θ.

Since the contact angle depends on the slope of the curve in the above data, the selected portion of the measurement data

may affect the contact angle value calculated from this slope. If the data were analyzed closer to the start of the experiment,

the slope would be greater than if the data near the end of the experiment were used. This would provide a lower contact

angle for the data selected at the start of the experiment than at the end of the experiment.

h to mto contact angle



THEORY OF NONWOVENS

c represents: pore structure, pore size and pore number in a solid porous material, for example, in a

nonwoven fabric

What does c mean? How to calculate value c?

First, another liquid of known contact angle with solid is used.

Typically, N-hexane is used which has a very low surface tension of 18.4mN / m and

usually has a 0 ° contact angle with solids.

Subsequently, the constant c of the nonwoven fabric to be tested is calculated. In a

further measurement, with the known constant c, a measurement is then made with the

desired liquid which does not have a zero contact angle.

The nonwoven fabric under study must be as uniform as possible, which may be a

problem at lower basis weights. Detailed statistical evaluation of acquired data is

necessary.



THEORY OF NONWOVENS

c represents: pore structure, pore size and pore number in a solid porous material, for example, in a nonwoven fabric

How to calculate value c?

N-hexane (contact angle 0°)

𝑚2 =𝑐𝜌2𝛾 𝑐𝑜𝑠𝜃

𝑡

y = ax; 𝑚2 = 𝑦; 𝑡 = 𝑥; 𝑎 =𝑐 𝜌2𝛾 𝑐𝑜𝑠𝜃

voda

cos 𝜃 =𝑎

𝒄 𝜌2𝛾

Determining (estimating) the contact angle for porous (fibrous) materials

THEORY OF NONWOVENS

𝒄 =𝑎ℎ𝑒𝑥𝑎𝑛𝑒

𝜌2𝛾 cos 𝜃=

0,08. 0,00033

429025 . 0,0184 . 1= 3,34 ∗ 10

− 9

N-hexane (contact angle 0°)

voda

HexaneViscosity 0,33mPasSurface tension 18,4mN/mDensity 655 kg/m3

𝑐𝑜𝑠𝜃 =0,0666 .0,001

3,34∗10−9 .1000 000 . 0,072= 0,274

Arccos 0,274 = 74,1°

cos 𝜃 =𝑎𝑤𝑎𝑡𝑒𝑟𝒄 𝜌2𝛾

WaterViscosity 1 mPasSurface tension72 mN/mDensity 1000 kg/m3

Example

THEORY OF NONWOVENS

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https://www.sciencedirect.com/science/article/pii/S0021979713000714http://iopscience.iop.org/article/10.1088/0957-0233/24/12/125902https://www.sciencedirect.com/science/article/pii/S0927775717311512

The same procedure can be used

for powdered materials. For Kruss it

is necessary to use a special

container in which the powder is

poured.

Contact angles are calculated from

the linear parts of the graphs at the

beginning of the measurement

(for very small h, respectively for

small m).

Contact angles greater than 90 °

cannot be determined in this way -

no wetting occurs.

Determining (estimating) the contact angle

for porous (fibrous) materials

THEORY OF NONWOVENS

https://www.sciencedirect.com/science/article/pii/S0021979713000714

http://iopscience.iop.org/article/10.1088/0957-0233/24/12/125902

https://www.sciencedirect.com/science/article/pii/S0927775717311512

Static x dynamic contact angle

Advancing x receding contact angle

http://www.weistron.com/products/contact-angle-meter/

1. Static contact angleStatic contact angles are

measured when a droplet is placed on the

surface and the three-phase boundary does not

move. A drop is placed on the solid surface and

the drop image is recorded. The static contact

angle is then defined by placing a Young-Laplace

equation around the droplet, although other

methods such as a circle and a polynomial may

be used. Static contact angles are used in quality

control, research and product development.

2. Dynamic contact angleWhen the three-phase

boundary moves, dynamic contact angles can be

measured. Contact angle hysteresis is the

difference between advancing and receding

contact angles. Contact angle hysteresis is based

on chemical and topographic surface

heterogeneity, surface impurities absorbed on the

surface, or swelling, rearrangement, or solvent

surface changes. Dynamic contact angles

indicate maximum and minimum static contact

values. Dynamic contact angles can be

measured using two different approaches:

changing the drop volume or using a tilting plane.

2. (1) Volume change method:In short, a small drop is

first created and placed on the surface. The needle is

then applied to the surface and the droplet volume is

gradually increased while recording the image. This

will provide a advancing contact angle. The receding

angle is measured in the same way, but this time the

droplet volume gradually decreases.

2. (2) The principle of the tilting plane method:The

drop is placed on the substrate, which is gradually

tilted. The advancing angle is measured on the front of

the drop just before the drop begins to move. The

receding contact angle is measured at the back of the

droplet at the same time point.



THEORY OF NONWOVENS

http://www.face-kyowa.co.jp/english/en_science/en_theory/en_what_contact_angle/

A generalized contact angle plot showing the advancing (qAdv) and receding (qRec) contact angleshttps://www.uweb.engr.washington.edu/research/tutorials/contact.html

https://www.youtube.com/watch?v=Qxe2gp3e1u8

Contact Angle Hysteresis is

due to:

Surface roughness

Chemical surface

heterogeneity

…

Velikost kapky



THEORY OF NONWOVENS

Determination of contactangle on swelling fiber

materials

A variety of experimental methods are availableto determine the contact angle of liquids on

solids. However, standard optical or Wilhelmy methods become difficult to apply when the

sample swells during wetting.

THEORY OF NONWOVENS

(a) Schematic of the swelling process of collagen structure consisting of fibers and fibrils. (b) SEM images of the collagen fiber before and after swelling due to water.

https://www.nature.com/articles/srep20563#f5

Fig. 1: Pulp fiber with swollen areas marked by

the circles and the corresponding degree of

swelling, i.e. the percentage of swollen fiber

length.

https://www.researchgate.net/figure/Pulp-fiber-with-swollen-areas-marked-by-the-circles-and-the-corresponding-degree-of_fig1_267694157

THEORY OF NONWOVENS

https://www.nature.com/articles/srep20563#f5

Determining (estimating) the contact angle of porous (fibrous) materials

Swelling of viscose hollow fibers in water

Botnání viskózových dutých vláken ve vodě Different types of fiber swelling according to geometric changes

- Fiber Diameter Increase ( D / D)

- Dial Fiber surface area increase ( A / A)

- Fiber length increase ( L / L)

- Axial Fiber volume increase ( V / V)

http://textilelearner.blogspot.com/2016/06/swelling-of-textile-fibers.html

THEORY OF NONWOVENS




THEORY OF NONWOVENS


An experiment with determining the contact angle

of water on a nonwoven that has been used to

produce feminine hygiene products.

When the fibers swell during wetting, the resulting

curve in the Washburn method is not linear even

at the beginning of the measurement.

It is necessary to proceed to indirectly determine

(estimate) the contact angle. Viscose nonwoven

+ water = not measurable directly === swelling

=== curve not linear. Indirect measurement of

contact angle.

1) Find liquids that can be directly measured, the

fibrous material in contact with them is not. For

example, organic solvents such as benzyl alcohol

(benzene methanol), diodomethane = viscose

fibers do not swell.


THEORY OF NONWOVENS

Indirect Contact Angle Measurement Procedure:

1) Finding liquids that can be directly measured

does not swell the fiber material in contact with

them. For example, organic solvents such as

benzyl alcohol (benzenemethanol),

diodomethane = viscose fibers do not swell.

2) Washburn method - direct dependence of the

m2/t curve on wetting with these organic solvents

3) Using Fowkes analysis - diodomethane is an

ideal candidate because it has a polar surface

tension component of zero.Tabulated values of polar and dispersion

components of surface tension.


THEORY OF NONWOVENS

Polar and dispersion components of surface tension

Fowkes equation

https://www.accudynetest.com/surface_tension_table.html


THEORY OF NONWOVENS

Polar and dispersion components of surface tension Fowkes equationhttps://www.accudynetest.com/surface_tension_table.html


THEORY OF NONWOVENS

Polar and dispersion components of surface tension Fowkes equation

There are several approaches that are used to calculate the surface tension, or surface energy, of solids

developed by a number of scientists.

Total surface energy of solids and liquids depends on various types of molecular

interactions such as dispersion (van der Waals), polar, and acid-base interactions.

The methods differ in the number of components or parameters they are equipped with. The most commonly used

theories are:

Zisman's theory

Fowkes method

Owens-Wendt-Rabel-Kaelble (OWRK) method

Wu theory

Acido-basic Van Oss method

Neumann Method

.


THEORY OF NONWOVENS

FOWKES'S THEORY

When two arbitrary phases contact each other, the Lifshitz-van der Waals force is applied;

1) Coulomb forces (molecules with distinct dipole - water, alcohols.

2) Inductive forces - inductively induced or strengthened dipoles are bound by electrostatic forces,

3) Dispersion forces - these forces correspond to the surface energy dispersion component

In fact, free surface energy is only divided into two parts: disperse and non-dispersive (including all

non-dispersive components).


THEORY OF NONWOVENS

FOWKES'S THEORY

The absence of a polar component in diiodomethane leads to

a simplification of the Fowkes equation

Calculation of disperse surface energy component

Subsequently, the polar surface energy component can be

calculated using benzyl alcohol in which both the polar and

dispersion components are known.

P


THEORY OF NONWOVENS

FOWKES'S THEORY

The absence of a polar component in diiodomethane leads to

a simplification of the Fowkes equation

If the surface energy of both solids components

has been calculated, the WATER contact angle

can be easily resolved by following the Fowkes

equation adjustment using standard WATER

surface tension values.


THEORY OF NONWOVENS

Swelling of hollow viscose fibers

Sometimes, the contact angle of the fluid due to swelling,

solubility, or any other similar problem cannot be directly

measured in the sample.

However, there is a method to determine this angle.

First, determine a set of solvents with different polar and

dispersion components (one of the components is zero in

one of the liquids) their surface tension, which does not

create a problem with the sample (do not swell, dissolve

the sample, etc.). (benzyl alcohol, diiodomethane)

Then calculate the surface energy of the sample using the

Fowkes method.

Once the surface energy (solids) of the sample is known,

these values, together with the surface tension values of

the problem fluid or solvent, can be used in the rearranged

Fowkes equation to indirectly determine the contact angle.

c c

c


THEORY OF NONWOVENS

Thank you for your attention!

THEORY OF NONWOVENS

Documents

Special application of wetting knowledge...Special application of wetting knowledge Wicking into fibrous materials CONTACT ANGLE ESTIMATION TNT Eva Kuželová Košťáková KCH, FP,